Feat v0.6.0 cluster registry + HA

PG-backed cluster registry for horizontal scaling — zero new
infrastructure (no etcd/Consul/Redis). MVP convergence point.

- node_registry UNLOGGED table (migration 013)
- Self-registration, heartbeat tick (10s), stale sweep (30s),
  self-eviction (os.Exit on 0 rows → K8s restarts)
- GET /api/v1/admin/cluster returns nodes with runtime stats
- Health endpoints include node_id + cluster size/peers
- cluster-dashboard admin surface with auto-refresh
- 3-replica E2E test (docker-compose-e2e.yml + ci/e2e-cluster-test.sh)
- chat + cluster-dashboard added to curated default bundle
- 5 new tests (3 unit + 2 handler), all passing

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

server/handlers/packages_bundled.go

@@ -23,13 +23,19 @@ import (
 )
 
 // defaultBundledPackages is the curated set of packages installed by default.
+// This is the dev/test bundle — includes demos and workflow examples.
 // Other packages still ship in the Docker image but require BUNDLED_PACKAGES
 // to be set explicitly (or "*" for all).
+//
+// Recommended production override (lean):
+//   BUNDLED_PACKAGES=notes,chat,chat-core,cluster-dashboard
 var defaultBundledPackages = map[string]bool{
 	"notes":                 true,
+	"chat":                  true,
 	"chat-core":             true,
 	"workflow-chat":         true,
 	"dashboard":             true,
+	"cluster-dashboard":     true,
 	"workflow-demo":         true,
 	"bug-report-triage":     true,
 	"content-approval":      true,