feat(shell): make module pages first-class top-level routes

Module pages move from `/modules/<id>` to `/<module-id>` (`/signage`),
beside `/settings` and `/account`, so the implementation concept
"module" never appears in a user-facing address. ADR 0057 is rewritten
to match.

- Core reserves the top-level names the platform actually serves today
  (`account`, `api`, `assets`, `display`, `settings`), and discovery
  refuses a module that declares one with `MODULE_ID_RESERVED`. That
  covers startup, `modules:validate`, and package verification. Tests in
  `apps/api` hold the set to every top-level route the API registers and
  every page the shell interprets.
- The API serves the Dashboard page at `/<module-id>` and below only for
  modules discovered with a Dashboard UI, enabled or not: a disabled
  module's bookmark still opens the Dashboard, which says it is
  unavailable. An arbitrary root path such as
  `/definitely-not-a-real-module` stays the sanitized 404.
- Both reference proxies forward every top-level path shaped like a
  module id and let the API decide; the split Dashboard hostname still
  refuses `/api`, `/display`, and `/assets`. Installing a module needs no
  proxy change.
- `/<module-id>/<page>` is already served and forwarded, so a later
  module sub-page contract needs no routing or deployment change; the
  shell shows "Page not found" there until it exists.
- The deploy smoke checks a module's address before install, while
  installed, while disabled, after removal, and after reinstall, plus
  unknown names and the old `/modules/…` form through the real proxy.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

surfaces/shell/scripts/build-browser.mjs

@@ -90,8 +90,8 @@ if (serve) {
   const context = await esbuild.context(buildOptions);
   await context.watch();
   // Any path with no file behind it gets the Dashboard page, so a refreshed deep link such as
-  // `/modules/example` reaches the shell's router here as it does from `apps/api` (ADR 0057).
-  // Development only: the API serves the page at exactly the Dashboard's reserved paths instead.
+  // `/example` reaches the shell's router here as it does from `apps/api` (ADR 0057).
+  // Development only: the API serves the page only at its platform pages and installed modules'.
   const { host, port } = await context.serve({
     fallback: path.join(outputDirectory, "index.html"),
     servedir: outputDirectory,