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]>

docs/development/api.md

@@ -260,12 +260,14 @@ have no redirect sink in this pass. See
 [ADR 0034](../architecture/decisions/0034-host-owned-browser-authentication.md).
 
 Since [ADR 0057](../architecture/decisions/0057-dashboard-urls-are-host-owned-routes.md) that URL
-is a real page address: the API serves the Dashboard page at `/` and anywhere under `/modules`,
-`/settings`, and `/account` (each bare and with everything below it), with the same bytes, validator,
-and headers as `/`. A deep link opened while signed out therefore shows the sign-in form at that
-address and opens its own page once the person signs in — still with no return value and no
-redirect. Any other path, including look-alikes such as `/settings-old`, remains the sanitized
-`404`.
+is a real page address: the API serves the Dashboard page at `/`, at `/settings` and `/account`, and
+at `/<module-id>` for every discovered module that declares a Dashboard UI (enabled or not) — each
+bare and with everything below it — with the same bytes, validator, and headers as `/`. A deep link
+opened while signed out therefore shows the sign-in form at that address and opens its own page once
+the person signs in — still with no return value and no redirect. Any other path — a module that is
+not installed, a display-only module, a look-alike such as `/settings-old` — remains the sanitized
+`404`. Module ids `account`, `api`, `assets`, `display`, and `settings` are reserved for the platform
+and refused by discovery (`MODULE_ID_RESERVED`).
 
 ### The four anonymous screens