feat(summary): revision-gated cache with stale-while-revalidate (STATE-WP-0066)

Replace the fixed 15s TTL on GET /state/summary with per-table revision
watermarks, stale-while-revalidate background refresh, and a progress-tail
section split. SQLAlchemy write hooks invalidate core or progress sections
on mutation. Adds tests, benchmark script, and operator docs.

Makefile

@@ -67,6 +67,10 @@ test-python:
 	TEST_DATABASE_URL=postgresql+asyncpg://custodian:changeme@127.0.0.1:5432/custodian_test \
 	$(UV) run pytest -x -q
 
+## Benchmark /state/summary revision cache (API must be running on :8000)
+benchmark-summary-cache:
+	$(UV) run python scripts/benchmark_summary_cache.py
+
 ## ops-bridge managed tunnels
 ## Requires ops-bridge: bridge is at /home/worsch/.local/bin/bridge
 tunnels-up: