feat(diagnostics): adicionar 16 ferramentas de diagnóstico DB Paperclip

14 tools read-only para inspecção da BD Paperclip directamente via MCP,
eliminando psql nos skills /clip-*. 2 tools write (rotation, cancel issue).

- src/db.ts: pool PG singleton + COMPANY_ID + helper query() parametrizado
- src/tools/diagnostics.ts: 16 tools, 100% queries com $1,$2 (zero injection)
- src/tools/index.ts: registo ...diagnosticsTools
- package.json: pg ^8.13.1 + @types/pg ^8.11.10
- CHANGELOG.md: changelog completo

Fix: diag_agents_without_membership cast a.id::text + filtros
principal_type='agent' AND status='active'.

Validado:
- 14/14 read tools testadas contra BD real (CEO=19 runs, 65 agentes,
  Reality Checker sem heartbeat/membership, 2 routines next_run_at NULL)
- npm audit: 0 vulnerabilidades
- grep '\${' em SQL: zero matches

Refs: Desk #2041

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

package.json

@@ -21,12 +21,14 @@
   "dependencies": {
     "@modelcontextprotocol/sdk": "^1.29.0",
     "dotenv": "^16.6.1",
+    "pg": "^8.13.1",
     "winston": "^3.19.0",
     "zod": "^3.25.76"
   },
   "devDependencies": {
     "@types/jest": "^30.0.0",
     "@types/node": "^22.19.17",
+    "@types/pg": "^8.11.10",
     "@typescript-eslint/eslint-plugin": "^7.18.0",
     "@typescript-eslint/parser": "^7.18.0",
     "eslint": "^8.57.1",