docs: add testing + release checklist; fix contributing links

docs/release/README.md

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+# Release checklist
+
+This is a lightweight, operator-friendly checklist for releasing Mission Control.
+
+> Goal: **no data loss** and **near-zero (ideally zero) user-visible downtime**.
+
+## Before you release
+
+- [ ] Confirm the target version/commit SHA.
+- [ ] Review merged PRs since last release (especially DB schema/auth changes).
+- [ ] Ensure CI is green on the target SHA.
+- [ ] Confirm you have:
+  - [ ] access to the host(s)
+  - [ ] access to Postgres backups (or snapshots)
+  - [ ] a rollback plan
+
+## Database safety
+
+- [ ] Verify migrations are **backward compatible** with the current running app (if doing rolling deploys).
+- [ ] Take a backup / snapshot.
+- [ ] If migrations are risky or not backward compatible, schedule a maintenance window.
+
+## Deploy (Docker Compose)
+
+- [ ] Pull / build the new images (or update the repo checkout).
+- [ ] Apply migrations (if you run them manually):
+
+```bash
+# example: if running backend locally on the host
+cd backend
+uv run alembic upgrade head
+```
+
+- [ ] Restart services with minimal disruption:
+
+```bash
+docker compose -f compose.yml --env-file .env up -d --build
+```
+
+## Post-deploy verification
+
+- [ ] Backend health: `GET /healthz` returns 200
+- [ ] Backend readiness: `GET /readyz` returns 200
+- [ ] Frontend loads (no console spam)
+- [ ] Login works (local/clerk mode)
+- [ ] Core flows work end-to-end:
+  - [ ] View board
+  - [ ] Create/update a task
+  - [ ] Post a comment
+  - [ ] Heartbeat check-in succeeds
+
+## Rollback (if needed)
+
+- [ ] Roll back the app version (compose / images).
+- [ ] If migrations were applied and are not reversible, rollbacks may require a DB restore.
+
+## Notes to keep this honest
+
+- If you add a new operational dependency (e.g., redis), update:
+  - `README.md` (overview + quickstart)
+  - `docs/deployment/README.md`
+  - this checklist