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/validations/modules.ts

@@ -0,0 +1,33 @@
+/**
+ * v1.18.0 — module enable/disable request validation.
+ *
+ * The PATCH body is a partial map of TOGGLEABLE module keys → boolean.
+ * Only keys in the canonical registry (`MODULE_KEYS`) are accepted; a
+ * core-domain key (`weight`, `bloodPressure`, `pulse`, `medications`) or
+ * any unknown key is a 422 — so the core measurement engine + meds can
+ * never be disabled through this surface (defence-in-depth on top of the
+ * gate, which has no key to flip for core domains anyway).
+ *
+ * `strict()` rejects unknown keys outright rather than silently dropping
+ * them, so a client gets a clear error instead of a no-op.
+ *
+ * The shared shape is reused by the OpenAPI registry so the wire
+ * contract stays single-source.
+ */
+import { z } from "zod/v4";
+
+import { MODULE_KEYS } from "@/lib/modules/registry";
+
+/** Build `{ <toggleableKey>?: boolean }` from the canonical key list. */
+const moduleShape = Object.fromEntries(
+  MODULE_KEYS.map((k) => [k, z.boolean().optional()]),
+) as Record<(typeof MODULE_KEYS)[number], z.ZodOptional<z.ZodBoolean>>;
+
+/**
+ * Partial module-preferences PATCH body. Every key is an optional
+ * boolean; omitted keys are left untouched server-side. `strict()`
+ * rejects any key not in `MODULE_KEYS` (including core domains).
+ */
+export const modulePrefsPatchSchema = z.object(moduleShape).strict();
+
+export type ModulePrefsPatch = z.infer<typeof modulePrefsPatchSchema>;