chore: mark fn-1.5 as done (Frontend WebSocket hook)

Task fn-1.5 completed - useTranscriptChat React hook already implemented in commit 2dfe82af.

Hook provides:
- WebSocket connection to /v1/transcripts/{id}/chat endpoint
- Token streaming with ref-based accumulation
- Message history management (user + assistant)
- Memory leak prevention with isMountedRef
- TypeScript type safety
- Proper WebSocket lifecycle and cleanup

Updated task documentation with acceptance criteria and evidence.

.flow/tasks/fn-1.5.json

@@ -1,14 +1,26 @@
 {
-  "assignee": null,
+  "assignee": "igor.loskutoff@gmail.com",
   "claim_note": "",
-  "claimed_at": null,
+  "claimed_at": "2026-01-13T00:45:16.020313Z",
   "created_at": "2026-01-12T22:41:17.754066Z",
   "depends_on": [],
   "epic": "fn-1",
+  "evidence": {
+    "commit": "2dfe82afbc26ab469915d02b61dcf0c66b0335d7",
+    "files": [
+      "www/app/(app)/transcripts/useTranscriptChat.ts"
+    ],
+    "verification": [
+      "TypeScript compilation successful (no errors for useTranscriptChat)",
+      "Proper WebSocket lifecycle management with cleanup",
+      "Memory leak prevention with isMountedRef",
+      "Type-safe Message and UseTranscriptChat interfaces"
+    ]
+  },
   "id": "fn-1.5",
   "priority": null,
   "spec_path": ".flow/tasks/fn-1.5.md",
-  "status": "todo",
+  "status": "done",
   "title": "Frontend WebSocket hook",
-  "updated_at": "2026-01-12T22:41:17.754248Z"
+  "updated_at": "2026-01-13T00:46:35.699645Z"
 }