fix(chat): clear stuck loading state across realtime lifecycle events

The chat UI could remain in a stale "Thinking/Processing" state when session IDs
did not line up exactly between view state (`currentSessionId`), selected route
session, pending session IDs, and provider lifecycle events. This was most visible
with Codex completion/abort flows, but the same mismatch risk existed in shared
handlers.

Unify lifecycle cleanup behavior in realtime handlers and make processing tracking
key off the active viewed session identity.

Changes:
- src/hooks/chat/useChatRealtimeHandlers.ts
- src/components/ChatInterface.tsx
- src/hooks/chat/useChatSessionState.ts

What changed:
- Added shared helpers in realtime handling:
  - `collectSessionIds(...)` to normalize and dedupe candidate session IDs.
  - `clearLoadingIndicators()` to consistently clear `isLoading`, abort UI, and status.
  - `markSessionsAsCompleted(...)` to consistently notify inactive/not-processing state.
- Updated lifecycle branches to use shared cleanup logic:
  - `cursor-result`
  - `claude-complete`
  - `codex-response` (`turn_complete` and `turn_failed`)
  - `codex-complete`
  - `session-aborted`
- Expanded completion/abort cleanup to include all relevant session IDs
  (`latestMessage.sessionId`, `currentSessionId`, `selectedSession?.id`,
  `pendingSessionId`, and Codex `actualSessionId` when present).
- Switched processing-session marking in `ChatInterface` to use
  `selectedSession?.id || currentSessionId` instead of `currentSessionId` alone.
- Switched processing-session rehydration in `useChatSessionState` to use
  the same active-view session identity fallback.

Result:
- Prevents stale loading indicators after completion/abort when IDs differ.
- Keeps processing session bookkeeping aligned with the currently viewed session.
- Reduces provider-specific drift by using one lifecycle cleanup pattern.

src/components/ChatInterface.tsx

@@ -232,10 +232,11 @@ function ChatInterface({
   }, [canAbortSession, handleAbortSession, isLoading]);
 
   useEffect(() => {
-    if (currentSessionId && isLoading && onSessionProcessing) {
-      onSessionProcessing(currentSessionId);
+    const processingSessionId = selectedSession?.id || currentSessionId;
+    if (processingSessionId && isLoading && onSessionProcessing) {
+      onSessionProcessing(processingSessionId);
     }
-  }, [currentSessionId, isLoading, onSessionProcessing]);
+  }, [currentSessionId, isLoading, onSessionProcessing, selectedSession?.id]);
 
   useEffect(() => {
     return () => {