feat(phase7): grow corpus, MCP write-tools+auth, /metrics observability

- content/: +5 real docs (caddy, bullmq, mcp-streamable-http, postgres-fts,
  cloudflare-525 writeup) across docs/writeups/notes. Reindexed: 9 docs, 17
  chunks, 5 revisions (was 4 docs).
- apps/mcp: add write-tools index_document/reindex_all/restore_revision (require
  x-webhook-secret) + queue_status (public). createMcpServer(authSecret?) threads
  the HTTP header; stdio keeps writes open (trusted local).
- apps/api: GET /metrics (Prometheus text: uptime + queue job gauges).
- Caddy: expose /metrics on wiki. domain -> :4020.
Verified live: /metrics 200; MCP tools/list -> 10; index_document unauth -> error,
auth -> enqueues + worker drains; typecheck green.

apps/mcp/package.json

@@ -16,6 +16,7 @@
   "dependencies": {
     "@mcpedia/config": "workspace:*",
     "@mcpedia/core": "workspace:*",
+    "@mcpedia/queue": "workspace:*",
     "@mcpedia/search": "workspace:*",
     "@modelcontextprotocol/sdk": "^1.29.0",
     "zod": "^4.0.0"