Task #207: custom subheadings inside executive-meeting attendee cells

Adds a new `kind` column (`varchar(16) NOT NULL DEFAULT 'person'`) on
`executive_meeting_attendees` so users can interleave free-text section
labels with person rows in a meeting's attendee list. Subheadings are
excluded from the running attendee number and from the per-meeting
attendee count surface, but reorder and delete identically to person
rows.

DB
- New `kind` column in `lib/db/src/schema/executive-meetings.ts`,
  defaulting to `"person"`. Applied via direct SQL because
  `drizzle-kit push` trips on a pre-existing duplicate-row issue in
  `app_permissions` (already documented in replit.md).

API (artifacts/api-server/src/routes/executive-meetings.ts)
- `attendeeSchema` accepts `kind: z.enum(["person","subheading"])` with
  default `"person"`.
- All 4 insert paths round-trip `kind`: POST create, PATCH meeting
  update (attendees replacement), PUT `/attendees`, and duplicate.
- `pdf-renderer` mapper forwards `kind`. `PdfMeetingAttendee.kind`
  typed as `string | null` to match the DB column shape.

Frontend (artifacts/tx-os/src/pages/executive-meetings.tsx)
- `AttendeeFlow` renders subheadings on a separate full-width row
  (`basis-full`, semibold, centered) and increments the running
  person index only for `kind === "person"`. Pending ghost row branches
  on `pendingKind`.
- Inline "+ subheading" chip via `onStartAdd(type, "subheading")`.
- Manage dialog: addSubheading button, subheading rows hide the title
  field, show a kind badge, and reorder/delete identically. Manage
  list summary count filters to person rows only (architect fix).
- Print page renders subheadings as `.em-print-subheading` and skips
  them in the running counter.
- New locale keys under `executiveMeetings.schedule` and
  `executiveMeetings.manage.attendees` in both `ar.json` and `en.json`.

PDF
- Subheadings print as `— label —` and never advance `personIdx`.

Tests
- New spec `executive-meetings-attendee-subheadings.spec.mjs` seeds
  mixed person+subheading rows and asserts (a) the subheading row
  renders, (b) numbering stays `1-`, `2-`, `3-` with a subheading
  wedged between persons, (c) zero-subheading meetings keep legacy
  numbering. Runs in both AR and EN. All 4 cases pass.

Code review
- Architect found one regression (Manage list summary count included
  subheadings) — fixed.

artifacts/tx-os/src/locales/ar.json

@@ -883,11 +883,14 @@
       "timeEnd": "وقت النهاية",
       "timeOrderError": "وقت النهاية قبل وقت البداية",
       "addAttendee": "أضف حاضر",
+      "addSubheading": "+ عنوان فرعي",
       "addVirtualAttendee": "+ حاضر عبر الاتصال المرئي",
       "addInternalAttendee": "+ حاضر داخلي",
       "addExternalAttendee": "+ حاضر خارجي",
       "newAttendeeAria": "اسم الحاضر الجديد",
       "editAttendeeAria": "تعديل اسم الحاضر",
+      "newSubheadingAria": "نص العنوان الفرعي الجديد",
+      "editSubheadingAria": "تعديل نص العنوان الفرعي",
       "deleteRow": "حذف الاجتماع",
       "deleteRowConfirm": "حذف هذا الاجتماع؟\n\n\"{{title}}\"\n\nلا يمكن التراجع عن هذا الإجراء.",
       "deleted": "تم حذف الاجتماع",
@@ -983,6 +986,9 @@
         "id": "رقم الحاضر",
         "type": "نوع الحضور",
         "add": "إضافة حاضر",
+        "addSubheading": "إضافة عنوان فرعي",
+        "subheadingName": "نص العنوان الفرعي",
+        "subheadingBadge": "عنوان فرعي",
         "remove": "إزالة",
         "moveUp": "تحريك للأعلى",
         "moveDown": "تحريك للأسفل",