refactor(review): address PR #185 review (lease leak, tests, changelog, jsonb seam)

8-point multi-aspect review of the batch PR; security/regressions were clean.

1. Lease leak: the #180 reorder moved `toolsFor` (which leases external MCP
   clients, refCount+1) ahead of buildSystemPrompt + forUser, but the only
   release (closeExternalClients) was bound to the streamText callbacks. A throw
   in between leaked the lease (refCount stuck, undici sockets held until
   restart). Define closeExternalClients right after the lease and wrap
   buildSystemPrompt+forUser in try/catch that closes-then-rethrows.
2. Cover the patch_node/delete_node dup-id refusal (#159 #6): extract the guard
   into a pure `assertUnambiguousMatch` (node-ops) and unit-test 0/1/>1.
3. Regress the body-before-title order (#159 #10): mock-HTTP test (collab fails
   fast against a server with no WS upgrade) asserts /pages/update (title) is
   NEVER posted when the body write fails — for updatePage AND updatePageJson.
4. CHANGELOG [Unreleased]: #180, #168 (Added); #163 (Fixed).
5. Add the missing en-US i18n keys (Back to references / {{label}}).
6. Drop the duplicate content/empty/blank cases in ai-chat.prompt.spec.ts (they
   repeat the buildMcpToolingBlock unit tests); keep only sandwich placement +
   both-safety-copies.
7. CI Postgres pg16 -> pg18 (match docker-compose).
8. jsonb decode seam: shared `parseJsonbValue(value, guard)` in database/utils.ts
   holds the legacy double-encoding self-heal in one place; parseToolAllowlist /
   parseModelConfig keep only a type-guard.

Verified: server build + 124 unit + 15 integration; mcp 311; prettier clean.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.github/workflows/test.yml

@@ -26,7 +26,7 @@ jobs:
     # TEST_*_URL overrides are needed.
     services:
       postgres:
-        image: pgvector/pgvector:pg16
+        image: pgvector/pgvector:pg18
         env:
           POSTGRES_USER: docmost
           POSTGRES_PASSWORD: docmost_dev_pw