fix: generate distinct task collaboration titles

Use verified task names until Agent generates a specific conversation title.
Repair legacy names without changing manual titles or history ordering.
Bound page repairs to 30 entries and a shared two-second deadline, and
re-read titles after task access validation to avoid stale reuse receipts.

Validation: bun run check; 40 focused tests across six files.

src/routes/chatStreamRoute.ts

@@ -1048,6 +1048,7 @@ export const registerChatStreamRoute = (
               latestAssistantMessage: assistantText,
               latestUserMessage: promptText,
               fallbackTitle: existingSessionTitle,
+              taskTitle: taskContext?.task.title,
             });
           }
           await sessionMetadataStore.touch(latestSessionRecord, {