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/developer-tools/DevelopTools.tsx

@@ -12,6 +12,7 @@ import {
   AccountDataSubmitCallback,
 } from '../../../components/AccountDataEditor';
 import { copyToClipboard } from '../../../utils/dom';
+import { getAccountData, setAccountData } from '../../../utils/accountData';
 import { AccountData } from './AccountData';
 import { CryptoDiagnostics } from '../developer/CryptoDiagnostics';
 
@@ -26,7 +27,7 @@ export function DeveloperTools({ requestClose }: DeveloperToolsProps) {
 
   const submitAccountData: AccountDataSubmitCallback = useCallback(
     async (type, content) => {
-      await (mx as any).setAccountData(type, content);
+      await setAccountData(mx, type, content);
     },
     [mx],
   );
@@ -36,7 +37,7 @@ export function DeveloperTools({ requestClose }: DeveloperToolsProps) {
       <AccountDataEditor
         type={accountDataType ?? undefined}
         content={
-          accountDataType ? (mx as any).getAccountData(accountDataType)?.getContent() : undefined
+          accountDataType ? getAccountData<object>(mx, accountDataType) : undefined
         }
         submitChange={submitAccountData}
         requestClose={() => setAccountDataType(undefined)}