feat(mcp): connect card, MCP docs, and an end-to-end roles/audit test over HTTP

MCP-8 #4972 "Connect card, docs, and end-to-end integration test".

- AI access page: a "Connect a client" card with the /mcp URL (from
  Settings → General → Public base URL, else the request host) and recipes
  for Claude Code, Claude Desktop (mcp-remote) and other Streamable HTTP
  clients, plus the reverse-proxy note. The token-created page shows the
  same recipes with the new token filled in, ready to paste.
- docs/core/mcp.md: connecting, the reverse-proxy requirements, the
  security model (token ceiling, default deny, check-mode default, secrets,
  audit), tools by role, response conventions, adding tools.
  docs/architecture.md describes the /mcp dispatch outside the blueprint
  pipeline; docs/reference/code-map.md gains an MCP section.
- tests/integration/test_mcp.py: over HTTP, a viewer token lists no write
  tools and is refused one by name; an operator token reads get_overview
  and its maintenance-window create/end land in the audit log as
  "<user> via MCP" with the token id. (Revoked → 401 was already covered.)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/architecture.md

@@ -44,6 +44,30 @@ All routes are Quart Blueprints registered in `app.py`:
 
 Plugin blueprints are mounted automatically by `load_plugins()` using the plugin directory name as the URL prefix.
 
+`/ai-access/` (`ai_access_bp`, `steward/ai_access/routes.py`) is where a signed-in user manages their API tokens.
+
+### `/mcp`: outside the blueprint pipeline
+
+`mount_mcp(app)` (`steward/mcp/server.py`) wraps `app.asgi_app`. A request to
+`/mcp` is handed to the MCP SDK's streamable-HTTP app before Quart sees it, so
+no blueprint, session cookie or `before_request` hook runs for it. Each
+request then goes through these steps:
+
+1. **Database gate.** If the database is unreachable, the request gets a 503
+   with a readable message.
+2. **Bearer resolution.** `api_tokens.resolve_token()` turns the token into a
+   `Caller` (user, effective role, token id). A missing, revoked or expired
+   token gets a 401.
+3. **Caller context.** The `Caller` and the app are set in ContextVars
+   (`steward/mcp/_context.py`). Tools read them through `current_caller()` and
+   `mcp_app()`, because Quart's `current_app` and `session` do not exist there.
+4. **Role gate.** `StewardMCPServer.refusal()` hides and refuses tools above
+   the caller's role, and plugin tools whose plugin is disabled.
+
+The SDK's session manager runs in Quart's `before_serving`/`after_serving`
+lifecycle. The server is stateless: no MCP session outlives a request. See
+[MCP server](core/mcp.md) for the security model and the tools.
+
 ---
 
 ## Scheduler