feat: add MCP runtime health dashboard to web UI (Closes #430)

Adds read-only /runtime and /api/runtime routes showing active profile,
identity, config model, git sync vs remote master, shell health,
workflow/schema hashes, and stale-runtime warnings with #420 guidance.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

docs/webui-local-dev.md

@@ -43,7 +43,8 @@ Optional environment variables:
 | `/api/projects` | JSON registry export |
 | `/prompts` | Prompt library with per-prompt copy buttons (#428) |
 | `/api/prompts` | JSON prompt export with workflow hashes |
-| `/runtime` | Stub — MCP runtime health (#430) |
+| `/runtime` | MCP runtime health and stale detection (#430) |
+| `/api/runtime` | JSON runtime health export |
 | `/audit` | Stub — report audit paste (#431) |
 | `/worktrees` | Stub — hygiene dashboard (#432) |
 | `/leases` | Stub — lease visibility (#433) |
@@ -82,8 +83,17 @@ credentials. The UI surfaces pagination proof (returned count, pages fetched,
 If credentials are missing or the fetch fails, the page shows an explicit error
 instead of an empty queue (fail closed).
 
+## Runtime health (#430)
+
+`/runtime` surfaces read-only MCP/runtime diagnostics for the default registry
+project: active profile and role kind, authenticated identity (when credentials
+are available), config model/mode, local vs remote `master` SHA sync, shell
+health, workflow/schema SHA-256 hashes, and stale-runtime warnings when the
+checkout is behind merged safety-gate changes. Restart guidance links to #420;
+no tokens or MCP restart actions are exposed.
+
 ## Tests
 
 ```bash
-pytest tests/test_webui_skeleton.py tests/test_webui_project_registry.py tests/test_webui_prompt_library.py tests/test_webui_queue_dashboard.py -q
+pytest tests/test_webui_skeleton.py tests/test_webui_project_registry.py tests/test_webui_prompt_library.py tests/test_webui_queue_dashboard.py tests/test_webui_runtime_health.py -q
 ```