Agent workspaces: per-contract overlays with instant handoff

- WorkspaceManager: create/get/list workspaces with daily/weekly/monthly/pinned tiers
- Saved searches: agent stores SQL queries in workspace context
- Shortlist: tag candidates/records to a workspace with notes
- Activity log: track calls, emails, updates per workspace per agent
- Instant handoff: transfer workspace ownership with full history
  Zero data copy — just a pointer swap, receiving agent sees everything
- Persistence: workspaces stored as JSON in object storage, rebuilt on startup
- Endpoints: /workspaces/create, /{id}, /{id}/handoff, /{id}/search,
  /{id}/shortlist, /{id}/activity
- Tested: Sarah creates workspace, saves searches, shortlists 3 candidates,
  logs activity, hands off to Mike who continues seamlessly

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

data/_catalog/manifests/142c4090-fd14-4065-8c06-d9721c14ec87.json

@@ -0,0 +1,15 @@
+{
+  "id": "142c4090-fd14-4065-8c06-d9721c14ec87",
+  "name": "candidates",
+  "schema_fingerprint": "auto",
+  "objects": [
+    {
+      "bucket": "data",
+      "key": "datasets/candidates.parquet",
+      "size_bytes": 10592165,
+      "created_at": "2026-03-27T13:43:21.924470705Z"
+    }
+  ],
+  "created_at": "2026-03-27T13:43:21.924477421Z",
+  "updated_at": "2026-03-27T13:43:21.924477421Z"
+}