MountedRoute class final

One route as it is actually served, for anything that inspects the app.

This is the whole introspection contract. A package that generates API documentation reads the method and path from here and finds its own description in metadata, which keeps dust_server free of any particular documentation format.

metadata is Object on purpose rather than a named type. An OpenAPI generator, a permissions audit, and a route-listing command each want something different in that slot, and naming one of them here would make the runtime depend on a format it has no business knowing. metadataOf is how a consumer takes its own type back and ignores everyone else's.

What this gives a documentation generator: every route, its method, and its path with {name} placeholders intact. What it deliberately does not give: parameter types and body schemas, which come from the build-time IR. This is introspection of the route table, not a schema source.