feat(19.7-02): identity kinds, ceilings, prompts and the MCP services page

- personal tokens only behind mcp.allow_personal_tokens (401 without a
  lookup otherwise); an admin token yields a backend-only identity with
  its scope limit per dispatched method, a user token a frontend-only one
- read/write ceiling and prompts proven by the tracer's subtests; the
  audit line asserted to carry the tool and never the arguments or token
- the mounted *pier.Pier is published on the application (test seams in
  export_test.go)
- docs/services/mcp.md with the tested acme.blog example, site.yaml note,
  cross-links from authentication.md, registration.md and the surf README

modules/surf/README.md

@@ -41,7 +41,7 @@ Use cases:
 - Request log, on by default: every request writes one Info record `http request` from the [diary](../diary/README.md) component `http` after it is served, with `method`, `pattern` (the matched route, such as `GET /posts/{id}`), `status`, `duration_ms` and `request_id` (the `X-Request-Id` header, trimmed and cut to 128 bytes, left out when empty). A request whose client went away adds `client_gone=true`; its 5xx is logged as 499 (client closed request) only when the client had already gone when the status was written and the handler did not panic, so a 5xx written before the cancellation and a recovered panic keep their real status. An unmatched request (a 404 or 405 from the mux, or a CORS preflight answered before routing) has an empty `pattern`. The URL path, the query string, headers and the client address are never logged, for an unmatched request too: a token route requested with another method answers 405 before any route handler runs. Records go to the app's published `*slog.Logger`, else the `http` component logger, whose channels all redact through [sunscreen](../sunscreen/README.md). Silence it with `log.components.http: warn` or turn it off with `http.access_log: false`.
 - Startup summary and shutdown report for `serve`: once it listens, a block on a terminal (version, environment, URL and admin URL, database host and name, pending migrations, plugins, queue, scheduler, mail, cache, realtime and search drivers; `-v` adds one line per plugin) and, off a terminal, the same facts as a `startup summary` record and a `listening on <addr>` record of component `serve`; after SIGINT or SIGTERM, a report of requests served, drained and aborted, worker jobs, uptime and drain errors. Never a DSN user or password.
 - Streaming routes: `surf.Router.MountStream` registers a raw route whose response is not buffered, so the handler's `http.Flusher` reaches the client while it is still running (server-sent events, long-lived streams). Named middleware, `body.limit`, locale, the CORS profile and the access-log pattern apply as on a raw route; a panic before the first byte answers an opaque 500 and after it only cuts the body short. Used by the MCP module; plugin route groups stay buffered.
-- MCP module hook: with `mcp.enabled` true, `surf.BuildRouter` calls the mount hook the MCP module sets in a binary built with the `surf.MCPBuildTag` tag (`summercms_mcp` in `summer.yaml` `build.tags`), after every plugin route and the admin exist. Off (the default) mounts nothing and changes nothing; on without the tag fails boot with an error naming the tag.
+- MCP module hook: with `mcp.enabled` true, `surf.BuildRouter` calls the mount hook the MCP module sets in a binary built with the `surf.MCPBuildTag` tag (`summercms_mcp` in `summer.yaml` `build.tags`), after every plugin route and the admin exist. Off (the default) mounts nothing and changes nothing; on without the tag fails boot with an error naming the tag. The tagged `pier_on.go` sets the hook with an adapter that gives [pier](../pier/README.md) the route table, `surf.Router.Handler`, `surf.Router.MountStream` and a plain GET mount for its metadata documents, so pier never imports surf; its routes are owned by `summercms.pier`.
 - A read-only route table (`surf.Router.Routes`), one route's compiled chain (`surf.Router.Handler`), the admin mount status (`surf.Router.AdminPrefix`) and the `serve` and `route:list` commands.
 
 ## Usage