DP16: add typed get/setAccountData helpers, remove ~19 any-casts

Add centralized typed helpers in src/app/utils/accountData.ts:
- getAccountData<T>(mx, eventType): T | undefined (returns content)
- setAccountData<T>(mx, eventType, content): Promise<void>

These wrap the single `as any` cast needed because matrix-js-sdk's typed
overloads reject the fork's custom account-data event names. Every call site
now stays fully typed on its content shape.

Route all account-data reads/writes that previously used
`(mx as any).getAccountData/setAccountData` or `mx.getAccountData(... as any)`
through the helpers (or, where a MatrixEvent is needed, through the existing
utils/room.ts getAccountData whose param is widened to accept string keys).
No behavior change: same event types, same content shapes.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/features/settings/account/Profile.tsx

@@ -35,6 +35,7 @@ import { SequenceCard } from '../../../components/sequence-card';
 import { SequenceCardStyle } from '../styles.css';
 import { SettingTile } from '../../../components/setting-tile';
 import { useMatrixClient } from '../../../hooks/useMatrixClient';
+import { getAccountData, setAccountData } from '../../../utils/accountData';
 import { presenceStateFromSetting } from '../../../hooks/usePresenceUpdater';
 import { useSetting } from '../../../state/hooks/settings';
 import { settingsAtom } from '../../../state/settings';
@@ -725,9 +726,7 @@ function ProfileTimezone() {
   const [savedTimezone, setSavedTimezone] = useState<string>('');
 
   useEffect(() => {
-    const cached = mx
-      .getAccountData('im.lotus.timezone' as any)
-      ?.getContent<{ timezone: string }>();
+    const cached = getAccountData<{ timezone: string }>(mx, 'im.lotus.timezone');
     if (cached?.timezone) {
       setTimezone(cached.timezone);
       setSavedTimezone(cached.timezone);
@@ -754,7 +753,7 @@ function ProfileTimezone() {
         Promise.all([
           // Self-fallback: account data is readable by useExtendedProfile for the
           // own user even on servers without extended-profile (m.tz) support.
-          (mx as any).setAccountData('im.lotus.timezone', { timezone: value }),
+          setAccountData(mx, 'im.lotus.timezone', { timezone: value }),
           // Mirror the pronouns write path so OTHER users can read the timezone
           // via the m.tz profile field. Best-effort: standard Synapse rejects
           // unknown profile fields, so a failure here must not fail the save.