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/manifest.json

@@ -0,0 +1,15 @@
+{
+  "id": "workflow-chat",
+  "title": "Workflow Chat",
+  "type": "library",
+  "tier": "starlark",
+  "version": "0.1.0",
+  "description": "Creates scoped chat conversations when workflow stages require team collaboration. Wire into stage_config as an on_advance hook.",
+  "author": "switchboard",
+
+  "permissions": ["db.write", "realtime.publish"],
+
+  "depends": ["chat-core"],
+
+  "exports": ["on_advance"]
+}