Feat v0.5.3 chat polish + integration testing

Conversation search (db.query search_like, chat-core /search endpoint,
sidebar search UI), message pagination polish (scroll preservation,
loading spinner), workflow-chat integration package, and multi-user
E2E test infrastructure.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/workflow-chat/README.md

@@ -0,0 +1,41 @@
+# Workflow Chat Integration
+
+Creates scoped chat conversations when workflow stages require team collaboration.
+
+## Setup
+
+1. Install the `workflow-chat` and `chat-core` packages.
+2. In your workflow stage with `audience: team`, set `stage_config`:
+
+```json
+{
+  "on_advance": {
+    "package_id": "workflow-chat",
+    "entry_point": "on_advance"
+  }
+}
+```
+
+3. When the workflow advances to that stage, ensure `stage_data` includes:
+
+```json
+{
+  "title": "Bug Triage Discussion",
+  "team_members": [
+    {"id": "user-1", "display_name": "Alice"},
+    {"id": "user-2", "display_name": "Bob"}
+  ],
+  "creator_id": "user-1",
+  "creator_display_name": "Alice"
+}
+```
+
+The hook will:
+- Create a group conversation titled `"Bug Triage Discussion [abcd1234]"` (suffixed with instance ID)
+- Add all team members as participants
+- Send a system message linking to the workflow instance
+- Enrich `stage_data` with the `conversation_id`
+
+## Idempotency
+
+If `stage_data` already contains a `conversation_id`, the hook returns `None` (no-op).