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/pages/client/sidebar/SpaceTabs.tsx

@@ -74,6 +74,7 @@ import {
   useSidebarItems,
 } from '../../../hooks/useSidebarItems';
 import { AccountDataEvent } from '../../../../types/matrix/accountData';
+import { setAccountData } from '../../../utils/accountData';
 import { ScreenSize, useScreenSizeContext } from '../../../hooks/useScreenSize';
 import { useNavToActivePathAtom } from '../../../state/hooks/navToActivePath';
 import { useOpenedSidebarFolderAtom } from '../../../state/hooks/openedSidebarFolder';
@@ -752,7 +753,7 @@ export function SpaceTabs({ scrollRef }: SpaceTabsProps) {
 
         const newSpacesContent = makeCinnySpacesContent(mx, newItems);
         localEchoSidebarItem(parseSidebar(mx, orphanSpaces, newSpacesContent));
-        (mx as any).setAccountData(AccountDataEvent.CinnySpaces, newSpacesContent);
+        setAccountData(mx, AccountDataEvent.CinnySpaces, newSpacesContent);
       },
       [mx, sidebarItems, setOpenedFolder, localEchoSidebarItem, orphanSpaces],
     ),
@@ -798,7 +799,7 @@ export function SpaceTabs({ scrollRef }: SpaceTabsProps) {
 
       const newSpacesContent = makeCinnySpacesContent(mx, newItems);
       localEchoSidebarItem(parseSidebar(mx, orphanSpaces, newSpacesContent));
-      (mx as any).setAccountData(AccountDataEvent.CinnySpaces, newSpacesContent);
+      setAccountData(mx, AccountDataEvent.CinnySpaces, newSpacesContent);
     },
     [mx, sidebarItems, orphanSpaces, localEchoSidebarItem],
   );