Schedule Core Hub stabilization checks for T02 sign-off

Add daily and closeout ActivityDefinitions, a manual stabilization script,
runbook, and workplan notes for the 2026-07-03 to 2026-07-10 window.

docs/deployment/stabilization-signoff.md

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+# Core Hub production stabilization
+
+Post-cutover checks for `CORE-WP-0007-T02` operator sign-off after
+`CORE-WP-0005` moved `hub.coulomb.social` to Core Hub (2026-07-03).
+
+## Window
+
+- **Start:** 2026-07-03 (production cutover)
+- **End:** 2026-07-10T17:35:00Z (closeout job)
+- **Daily job:** 09:00 Europe/Berlin via activity-core
+
+## Automated checks
+
+The `core-hub` context resolver query `stabilization_check` verifies:
+
+| Check | Expected |
+| --- | --- |
+| `GET /healthz` | 200 |
+| `GET /readyz` | 200 |
+| `GET /api/v2/widget-types` | 200, count ≥ 26 |
+| `GET /api/v2/hubs` (unauthenticated) | 401 |
+
+State Hub progress events:
+
+- `core_hub_stabilization_check` — daily while the window is open
+- `core_hub_stabilization_closeout` — one-shot at window end
+
+Activity definitions live in `activity-definitions/` and are projected into
+`activity-core/k8s/railiance/20-runtime.yaml`.
+
+## Manual companion script
+
+```bash
+CORE_HUB_BASE_URL=https://hub.coulomb.social \
+STATE_HUB_URL=http://127.0.0.1:8000 \
+./scripts/core_hub_stabilization_check.sh
+```
+
+Optional full bootstrap smoke (needs approved operator token):
+
+```bash
+CORE_HUB_BASE_URL=https://hub.coulomb.social \
+CORE_HUB_OPERATOR_TOKEN_FILE=/secure/path/to/token \
+make deployed-smoke
+```
+
+## Operator sign-off for T02
+
+Sign-off is a human decision recorded in State Hub after:
+
+1. Daily checks (or closeout) show `overall_pass=true` through the window
+2. No rollback was invoked since cutover
+3. Operator approves retiring the Inter-Hub k8s rollback deployment
+
+Post a progress note or decision referencing workstream
+`a8d66822-e435-4b1e-ad81-37a298d1795e` / task `16eb7ce3-b574-4667-a189-c14ff5d0502b`,
+then proceed with `CORE-WP-0007-T02`.
+
+## Deploy / enable
+
+1. Rebuild and deploy `activity-core` on railiance01 with the new `core-hub`
+   context resolver.
+2. Apply the updated `activity-core/k8s/railiance/20-runtime.yaml` ConfigMap
+   projection for the two new ActivityDefinitions.
+3. Confirm events appear at `GET /progress/?event_type=core_hub_stabilization_check`.