Task #204: Make attendee group headers more prominent

Original ask: in the executive-meetings schedule's attendee cell, the
"Virtual / Internal / External Attendance" group labels (rendered above
each attendee group) read like stray attendee names — text-xs with em-dash
decoration. The user wanted them to stand out visually as section labels.

Changes
- artifacts/tx-os/src/pages/executive-meetings.tsx (AttendeeGroup):
  * Header now renders text-sm font-bold, navy color (#0B1E3F), centered.
  * Hairline underline (border-b border-[#0B1E3F]/15) with explicit
    print:border-b print:border-gray-400 fallback so the underline is
    preserved on print stylesheets that strip translucent borders.
  * Em-dash decoration removed from the label.
  * pointer-events-none + select-none so clicks/selection target the
    attendee names, not the label.
  * Added stable data-testid="em-attendee-group-header" for tests.

Tests
- New spec artifacts/tx-os/tests/executive-meetings-attendee-group-headers.spec.mjs:
  * Seeds its OWN multi-group meeting (2 virtual + 3 internal) on a unique
    far-future date per locale (offsets 1/2) — never collides with real
    schedule data.
  * Asserts BOTH expected localised headers appear (virtual + internal),
    and that the external header is absent.
  * Adds a regression guard: a single-group (all-internal) meeting on a
    different unique future date renders ZERO group headers.
  * Temporarily flips admin's preferred_language per-test (with try/finally
    + afterAll restore) so AuthContext does not override the locale via
    i18n.changeLanguage on auth restore.
- Existing executive-meetings-edit-toggle.spec.mjs still passes (6/6).
- All 4 new tests pass.

Drift / deviations
- The original draft test lived inline in the toggle spec and skipped
  because today's seed data has no multi-group meetings. Moved it to its
  own spec with self-seeded data per code-review feedback so coverage is
  deterministic, header assertions are tightened (require both expected
  labels, reject the external one, not "any two of three"), and a
  single-group regression guard is added.

artifacts/tx-os/tests/executive-meetings-attendee-group-headers.spec.mjs

@@ -1,5 +1,27 @@
 import { test, expect } from "@playwright/test";
 import pg from "pg";
+import { readFileSync } from "node:fs";
+import { fileURLToPath } from "node:url";
+import { dirname, join } from "node:path";
+
+const __dirname = dirname(fileURLToPath(import.meta.url));
+
+// Load expected header strings from the SAME locale bundles the app
+// renders from, so the assertions stay in sync if the copy ever
+// changes.
+function loadLocale(lang) {
+  const p = join(__dirname, "..", "src", "locales", `${lang}.json`);
+  return JSON.parse(readFileSync(p, "utf8"));
+}
+const localeBundles = { en: loadLocale("en"), ar: loadLocale("ar") };
+function attendanceLabel(lang, kind) {
+  const em = localeBundles[lang]?.executiveMeetings;
+  if (!em) throw new Error(`Missing executiveMeetings namespace in ${lang}.json`);
+  const key = `${kind}Attendance`; // virtualAttendance | internalAttendance | externalAttendance
+  const val = em[key];
+  if (!val) throw new Error(`Missing locale key executiveMeetings.${key} in ${lang}.json`);
+  return val;
+}
 
 // E2E coverage for Task #204: the per-group attendee headers
 // ("Virtual Attendance / Internal Attendance / External Attendance")
@@ -201,13 +223,11 @@ for (const lang of ["en", "ar"]) {
       // match because the virtual header may be suffixed with the
       // platform name, e.g. " — Zoom"). This rejects any regression
       // that drops a header, mislabels a group, or renders the same
-      // label twice.
-      const virtualLabel =
-        lang === "ar" ? "الحضور عبر الاتصال المرئي" : "Virtual Attendance";
-      const internalLabel =
-        lang === "ar" ? "الحضور الداخلي" : "Internal Attendance";
-      const externalLabel =
-        lang === "ar" ? "حضور خارجي" : "External Attendance";
+      // label twice. Labels are read from the SAME locale bundle the
+      // app renders from so copy edits won't silently break the spec.
+      const virtualLabel = attendanceLabel(lang, "virtual");
+      const internalLabel = attendanceLabel(lang, "internal");
+      const externalLabel = attendanceLabel(lang, "external");
 
       const seenTexts = [];
       for (let idx = 0; idx < 2; idx++) {