feat: MCP ping tool, tightened descriptions, and Hermes client docs

- Add  MCP tool — lightweight connectivity check returning server
  identity, no DB hit (resolves agent connection-test friction)
- Tighten 6 tool descriptions (get_relations, get_health_summary,
  query_metrics, get_trend, get_event_timeline, ping) to be searchable
  in the first 8-12 words
- Document Hermes MCP client setup in ADR-0012 with token security caveat
- Move completed plan to plans/done/

plans/index.md

@@ -19,6 +19,7 @@ went sideways, open an investigation.
 | 2026-07-17 | [Codebase review, lint audit, and documentation maintenance](2026-07-17-codebase-review-and-cleanup.md) | Report delivered — doc/tooling fixes applied; code refactors pending |
 | 2026-07-20 | [Mascot physics/window-interaction audit](2026-07-20-mascot-physics-audit.md) | P0–P2 implemented; P3 ("cool stuff") ideas open |
 | 2026-07-21 | [Frontend as OS + Apps — architecture audit & refactor](2026-07-21-frontend-os-apps-architecture.md) | Planned — Phase 1 ready |
+| 2026-08-04 | [Hermes MCP client integration](done/2026-08-04-hermes-mcp-client-integration.md) | Done — deployed |
 
 ## Done
 
@@ -73,4 +74,4 @@ See [`done/`](done/) for executed plans:
 - File name: `YYYY-MM-DD-<slug>.md`. Use the *target* date if known, otherwise the planning date.
 - Status: `Planned` → `In Progress` → `Done` (move to `done/` on completion).
 - When done: add a changelog entry on every affected node page, then move the file to `done/`.
-- Plans are append-only once execution starts — don't rewrite pre-flight intent after the fact.
+- Plans are append-only once execution starts — don't rewrite pre-flight intent after the fact.