fix: comprehensive P0 quality pass — audit findings resolved

- ReportRoomModal: use mx.reportRoom() SDK method, fix undefined CSS vars
  (--mx-surface/border → folds color tokens), add role/aria-modal/aria-labelledby,
  accessible select/input labels, per-error-code messages, auto-close on success
- About.tsx: clickable matrix_id + email_address links (Text as="a"), AbortController
  cleanup, runtime JSON type guard, loading state, role display for all role values,
  remove classList theming hack, use mx.getHomeserverUrl()
- RoomViewHeader: useLocalRoomName for header title, useReportRoomSupported gate,
  hide Invite/Settings/Report for server notice rooms, isCreator guard on Report,
  FocusTrap returnFocusOnDeactivate on topic overlay, Server Notice chip tooltip
- RoomInput: replace raw <div> with folds <Box> for server notice read-only message
- EditHistoryModal: isRawEditEvent type guard, handle next_batch truncation,
  getVersionBody handles formatted_body (strips HTML for text display),
  role/aria-modal/aria-labelledby accessibility, guard for undefined eventId,
  use config.space tokens (remove var(--mx-spacing-*) strings)
- RoomNavItem: remove duplicate getExistingContent (use exported getLocalRoomNamesContent),
  maxLength={255} on rename input, fix FocusTrap nesting (renameDialog state moved to
  RoomNavItem_, RenameRoomDialog rendered outside menu, menu closes before dialog opens),
  pencil icon opacity via config.opacity.P300
- useRoomMeta: export getLocalRoomNamesContent for reuse
- RoomIntro: useLocalRoomName, formatted topic viewer with Overlay/FocusTrap/RoomTopicViewer
- CallRoomName: useLocalRoomName for consistent rename display in call overlay
- General.tsx: fix #980000/#FF6B00 hardcoded hex → color tokens/CSS vars, URL Preview
  capitalization, improved encrypted preview warning text + Warning chip, add
  description to plain urlPreview setting
- sanitize.ts: fix hex color regex to support 3/4/6/8 digit hex (CSS4 #RGBA, #RRGGBBAA)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/app/features/room/RoomInput.tsx

@@ -605,11 +605,17 @@ export const RoomInput = forwardRef<HTMLDivElement, RoomInputProps>(
 
     if (room.getType() === 'm.server_notice') {
       return (
-        <div ref={ref} style={{ padding: config.space.S300, textAlign: 'center' }}>
+        <Box
+          ref={ref as React.Ref<HTMLDivElement>}
+          direction="Column"
+          alignItems="Center"
+          justifyContent="Center"
+          style={{ padding: config.space.S300 }}
+        >
           <Text size="T300" priority="300">
-            This is a server notice room — you cannot send messages here.
+            This room contains system messages from your homeserver. Replies are not permitted.
           </Text>
-        </div>
+        </Box>
       );
     }