feat(api): surface and update per-user module preferences

GET /api/auth/me now returns a resolved modules map for every toggleable
module (cycle/coach reflect their delegated state). New PATCH/GET
/api/auth/me/modules read and update the preferences: the body is strict
over the toggleable key set so a core-domain or unknown key is a 422, the
merge is field-by-field (no mass assignment), and userId is narrowed from
the session. Documented in the OpenAPI registry and yaml.

The disable-coach gate-inventory allowlist records the module gate's
intentional coach delegation read.

src/lib/feature-flags/__tests__/coach-user-disable.test.tsx

@@ -317,6 +317,12 @@ describe("Coach per-user disableCoach invariant", () => {
     // builder.
     "src/lib/dashboard/snapshot.ts",
     "src/app/api/dashboard/snapshot/route.ts",
+    // v1.18.0 — the module enable/disable gate delegates the `coach`
+    // module to the SAME two-layer source of truth (`user.disableCoach`
+    // AND the operator assistant master flag) rather than owning a
+    // second copy in `modulePreferencesJson`. Covered by the coach-
+    // delegation cases in `src/lib/modules/__tests__/gate.test.ts`.
+    "src/lib/modules/gate.ts",
   ];
 
   /**