fix(desktop): component cleanup + dead code removal + DeerFlow ai-elements

- ChatArea: DeerFlow ai-elements annotations for accessibility
- Conversation: remove unused Context, simplify message rendering
- Delete dead modules: audit-logger.ts, gateway-reconnect.ts
- Replace console.log with structured logger across components
- Add idb dependency for IndexedDB persistence
- Fix kernel-skills type safety improvements

desktop/src/lib/secure-storage.ts

@@ -277,28 +277,6 @@ function clearLocalStorageBackup(key: string): void {
   }
 }
 
-// Keep synchronous versions for backward compatibility (deprecated)
-function writeLocalStorageBackup(key: string, value: string): void {
-  try {
-    if (value) {
-      localStorage.setItem(key, value);
-    } else {
-      localStorage.removeItem(key);
-    }
-  } catch (e) {
-    logger.debug('writeLocalStorageBackup failed', { error: e });
-  }
-}
-
-function readLocalStorageBackup(key: string): string | null {
-  try {
-    return localStorage.getItem(key);
-  } catch (e) {
-    logger.debug('readLocalStorageBackup failed', { error: e });
-    return null;
-  }
-}
-
 // === Device Keys Secure Storage ===
 
 /**