#635: External meetings + auto-numbering

User asked for three things in the executive-meetings module:
1. Remove the "daily number" input from the add/edit dialog — numbering
   is auto-assigned by the server already, so the field was just noise.
2. Add an "اجتماع خارجي" (external meeting) toggle. When ON, the row
   is force-tinted red in the schedule grid.
3. External meetings must be excluded from the auto-postpone flow:
   the alert "Postpone" button is disabled, and the cascade shift
   skips them as followers.

Changes
- lib/db/src/schema/executive-meetings.ts
  + `is_external boolean not null default false` column. Pushed via
    drizzle-kit (no destructive migration; defaults backfill).
- artifacts/api-server/src/routes/executive-meetings.ts
  + `isExternal` added to base zod fields, POST insert, PATCH update.
  + POST/PATCH force `rowColor='red'` when `isExternal=true`.
  + POST /:id/postpone-minutes rejects external meetings with
    HTTP 409 + code `external_meeting_no_auto_postpone`.
  + `computeCascadeShift` filters out external followers (preview +
    writer stay in lockstep, as the comment promises).
- artifacts/tx-os/src/pages/executive-meetings.tsx
  + Meeting type + MeetingFormState gain `isExternal`; dropped the
    `dailyNumber` field from the form state entirely.
  + `emptyMeetingForm` / `openEdit` updated; ManageSection.save() and
    the inline ScheduleSection save body now send `isExternal` and
    never send `dailyNumber`.
  + MeetingFormDialog: removed the daily-number FormRow and added a
    Switch-based external-meeting FormRow with localized hint.
  + `rowColors` memo coerces to "red" whenever `m.isExternal`.
  + Audit-diff "interesting" list now includes `isExternal`.
- artifacts/tx-os/src/components/executive-meetings/upcoming-meeting-alert.tsx
  + Meeting type gains optional `isExternal`.
  + "Postpone" button disabled + tooltip when meeting is external.
- locales: added `field.isExternal`, `field.isExternalHint`,
  `field.isExternalOn/Off`, and `alert.externalCannotPostpone` in
  both ar.json and en.json. Existing dailyNumber keys kept (still
  referenced by the manage-table column header / cell display).

Post-review hardening (from architect pass)
- PATCH now coerces rowColor → 'red' for any PATCH that touches a row
  that is (or becomes) external. Prevents PDF/export paths that read
  raw rowColor from showing a non-red tint for externals.
- Schedule row quick-actions popover: the "Postpone" button is now
  disabled with a localized tooltip when the meeting is external,
  matching the upcoming-meeting alert behavior.
- PostponeDialog.handleErr maps the 409 code
  `external_meeting_no_auto_postpone` to the localized
  `alert.externalCannotPostpone` toast so users see a real reason
  instead of the raw English error string.

Notes
- The `dailyNumber` column stays in DB (heavily used for slot
  persistence and the unique index); only the form input was removed.
  Server's `nextDailyNumber()` already auto-assigns when the field is
  absent on POST, and PATCH leaves it untouched when absent.
- Two pre-existing TS errors remain in api-server (`isHighlighted`
  type-inference quirk on `z.union(...).transform(...)` and a
  font_settings comparison) — not in scope for this task.
- Tests not added; verification by typecheck on changed surfaces and
  workflow-restart smoke. No e2e harness was wired.

artifacts/tx-os/src/pages/executive-meetings.tsx

@@ -194,6 +194,10 @@ type Meeting = {
   // is the same for every viewer. NULL/missing = "default" (no tint).
   // Allowed values come from ROW_COLOR_OPTIONS below.
   rowColor?: string | null;
+  // #635: External meeting flag. When true, the row is force-tinted red
+  // and the alert-postpone button is disabled (the server also rejects
+  // /postpone-minutes with `external_meeting_no_auto_postpone`).
+  isExternal?: boolean;
   // #486: optimistic-lock token used by /executive-meetings/swap-times
   // (the schedule row quick-actions Move up / Move down popover) and
   // by the existing PostponeDialog when reused from the schedule.
@@ -1361,7 +1365,12 @@ function ScheduleSection({
   const rowColors = useMemo<Record<number, string>>(() => {
     const out: Record<number, string> = {};
     for (const m of meetings) {
-      if (m.rowColor) out[m.id] = m.rowColor;
+      // #635: external meetings are always tinted red regardless of
+      // (and overriding) any manually-set rowColor, so the visual cue
+      // matches the flag even on legacy rows whose rowColor was set
+      // before isExternal existed.
+      if (m.isExternal) out[m.id] = "red";
+      else if (m.rowColor) out[m.id] = m.rowColor;
     }
     return out;
   }, [meetings]);
@@ -3403,10 +3412,9 @@ function ScheduleSection({
                 sortOrder: idx,
                 kind: a.kind ?? "person",
               })),
+              // #635: external meeting flag.
+              isExternal: editingMeeting.isExternal,
             };
-            if (editingMeeting.dailyNumber.trim()) {
-              body.dailyNumber = Number(editingMeeting.dailyNumber);
-            }
             try {
               await apiJson(
                 `/api/executive-meetings/${editingMeeting.id}`,
@@ -4984,6 +4992,12 @@ function MeetingRow({
                   setQuickOpen(false);
                   onQuickPostpone?.();
                 }}
+                disabled={meeting.isExternal}
+                title={
+                  meeting.isExternal
+                    ? t("executiveMeetings.alert.externalCannotPostpone")
+                    : undefined
+                }
                 className={`flex-1 min-w-0 gap-2 px-3 py-2 h-10 text-sm font-medium shadow-sm ${isRtl ? "flex-row-reverse" : ""}`}
                 data-testid={`em-row-quick-postpone-${meeting.id}`}
               >
@@ -6266,7 +6280,6 @@ type MeetingFormState = {
   titleAr: string;
   titleEn: string;
   meetingDate: string;
-  dailyNumber: string;
   startTime: string;
   endTime: string;
   location: string;
@@ -6276,6 +6289,9 @@ type MeetingFormState = {
   isHighlighted: boolean;
   notes: string;
   attendees: Attendee[];
+  // #635: external meeting flag — when true the row is force-tinted red
+  // and the alert-postpone button is disabled.
+  isExternal: boolean;
 };
 
 // Generate a stable client-only attendee id for the manage-dialog DnD.
@@ -6294,7 +6310,6 @@ function emptyMeetingForm(date: string): MeetingFormState {
     titleAr: "",
     titleEn: "",
     meetingDate: date,
-    dailyNumber: "",
     startTime: "",
     endTime: "",
     location: "",
@@ -6304,6 +6319,7 @@ function emptyMeetingForm(date: string): MeetingFormState {
     isHighlighted: false,
     notes: "",
     attendees: [],
+    isExternal: false,
   };
 }
 
@@ -6602,7 +6618,6 @@ function ManageSection({
       titleAr: htmlToPlainText(m.titleAr),
       titleEn: htmlToPlainText(m.titleEn ?? ""),
       meetingDate: m.meetingDate,
-      dailyNumber: String(m.dailyNumber),
       startTime: m.startTime ? m.startTime.slice(0, 5) : "",
       endTime: m.endTime ? m.endTime.slice(0, 5) : "",
       location: m.location ?? "",
@@ -6622,6 +6637,7 @@ function ManageSection({
         name: htmlToPlainText(a.name),
         _sid: genAttendeeSid(),
       })),
+      isExternal: m.isExternal ?? false,
     });
   }
 
@@ -6675,8 +6691,10 @@ function ManageSection({
         // schedule survive a save through the Manage dialog.
         kind: a.kind ?? "person",
       })),
+      // #635: send the external flag so the server can force rowColor='red'
+      // and the cascade/postpone rules know to skip it.
+      isExternal: editing.isExternal,
     };
-    if (editing.dailyNumber.trim()) body.dailyNumber = Number(editing.dailyNumber);
     try {
       if (editing.id == null) {
         await apiJson(`/api/executive-meetings`, { method: "POST", body });
@@ -7553,16 +7571,26 @@ function MeetingFormDialog({
               onChange={(e) => update("meetingDate", e.target.value)}
             />
           </FormRow>
+          {/* #635: external-meeting toggle replaces the daily-number
+              input (numbering is now fully auto-assigned by the
+              server). When ON the row is force-tinted red and the
+              alert-postpone button is disabled. */}
           <FormRow
-            label={t("executiveMeetings.manage.field.dailyNumber")}
-            hint={t("executiveMeetings.manage.field.dailyNumberHint")}
+            label={t("executiveMeetings.manage.field.isExternal")}
+            hint={t("executiveMeetings.manage.field.isExternalHint")}
           >
-            <Input
-              type="number"
-              min={1}
-              value={state.dailyNumber}
-              onChange={(e) => update("dailyNumber", e.target.value)}
-            />
+            <div className="flex items-center gap-2 h-9">
+              <Switch
+                checked={state.isExternal}
+                onCheckedChange={(v) => update("isExternal", Boolean(v))}
+                data-testid="em-form-isExternal"
+              />
+              <span className="text-xs text-gray-700">
+                {state.isExternal
+                  ? t("executiveMeetings.manage.field.isExternalOn")
+                  : t("executiveMeetings.manage.field.isExternalOff")}
+              </span>
+            </div>
           </FormRow>
           <FormRow
             label={t("executiveMeetings.manage.field.startTime")}
@@ -7843,6 +7871,7 @@ function AuditDiffSummary({
     "platform",
     "status",
     "isHighlighted",
+    "isExternal",
     "notes",
     "assignedTo",
     "taskType",