#262: remove Requests / Approvals / Tasks tabs from Executive Meetings

Full-stack removal of the three retired sections, including the
canApprove capability flag.

Backend
- routes/executive-meetings.ts: deleted /requests* + /tasks* handlers,
  REQUEST_ROLES / TASK_VIEW_ROLES / TASK_BROAD_VIEW_ROLES, the four
  retired capability flags from /me, retired imports, and dead schemas
  (detailsByType, request*Schema, taskCreateSchema, taskPatchSchema,
  dueAtSchema, dateOnly, timeHm). Renamed APPROVE_ROLES → EM_ADMIN_ROLES;
  /me now returns canEditGlobalFontSettings (true server-side gate for
  the only surviving consumer). Dropped now-unused requireApprove export.
- lib/executive-meeting-notify.ts: types collapsed to ['meeting_created'].

Frontend
- pages/executive-meetings.tsx: deleted Requests/Approvals/Tasks
  sections, RequestListRow, retired SECTIONS entries, MeRoles type,
  unused icon imports. MeCapabilities.canApprove → canEditGlobalFontSettings.
- hooks/use-notifications-socket.ts: dropped two retired invalidations.
- locales/{ar,en}.json: removed nav + section + 6 retired type keys.

Schema + DB
- lib/db/src/schema/executive-meetings.ts: tables/relations removed.
- scripts/cleanup-em-requests-tasks.sql: idempotent cleanup — orphan
  prefs / notifications / audit rows then DROP TABLE … CASCADE.
  Applied to dev DB; `db push` re-synced.

Tests
- Sequential `node --test --test-concurrency=1` → 226/226 pass.
- /me test now asserts canApprove + 3 retired flags absent and the new
  canEditGlobalFontSettings flag is present.

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

@@ -233,7 +233,7 @@ type MeCapabilities = {
   roles: string[];
   canRead: boolean;
   canMutate: boolean;
-  canApprove: boolean;
+  canEditGlobalFontSettings: boolean;
   canViewAudit: boolean;
 };
 
@@ -661,7 +661,7 @@ export default function ExecutiveMeetingsPage() {
         {section === "fontSettings" && me && (
           <FontSettingsSection
             font={effectiveFont}
-            canEditGlobal={me.canApprove}
+            canEditGlobal={me.canEditGlobalFontSettings}
             t={t}
           />
         )}