Feat v0.6.4 admin health/metrics tab + cluster merge

Admin Health tab under Monitoring with auto-refreshing runtime, DB,
cluster, and extension metrics panels. New GET /api/v1/admin/metrics
endpoint. Fattened heartbeat JSONB with stack, GC CPU%, extension
count, sandbox stats, trigger fires. Sandbox runner and trigger engine
now track cumulative execution counters. Event bus tracks publish/deliver
counts. Health endpoints consolidated via shared builder. Block renderers
(mermaid, katex, csv-table, diff-viewer) no longer require chat.
cluster-dashboard package retired — merged into admin Health tab.

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

packages/csv-table/manifest.json

@@ -6,7 +6,7 @@
     "tier": "browser",
     "author": "switchboard",
     "description": "Renders ```csv code blocks as sortable, interactive HTML tables",
-    "requires": ["chat"],
+    "requires": [],
     "permissions": [],
     "tools": [],
     "surfaces": [],