Shared + migration: table user_preference (thème clair/sombre/système) (step 1/4)

- Modèle Prisma UserPreference (1-1 avec UserProfile, onDelete Cascade),
  enum ThemePreference (LIGHT/DARK/SYSTEM, défaut SYSTEM)
- packages/shared: THEME_PREFERENCES/ThemePreference, PreferencesView,
  updatePreferencesSchema

apps/api/prisma/migrations/20260817120000_add_user_preference/migration.sql

@@ -0,0 +1,13 @@
+-- CreateEnum
+CREATE TYPE "ThemePreference" AS ENUM ('LIGHT', 'DARK', 'SYSTEM');
+
+-- CreateTable
+CREATE TABLE "user_preference" (
+    "user_profile_id" INTEGER NOT NULL,
+    "theme" "ThemePreference" NOT NULL DEFAULT 'SYSTEM',
+
+    CONSTRAINT "user_preference_pkey" PRIMARY KEY ("user_profile_id")
+);
+
+-- AddForeignKey
+ALTER TABLE "user_preference" ADD CONSTRAINT "user_preference_user_profile_id_fkey" FOREIGN KEY ("user_profile_id") REFERENCES "user_profiles"("id") ON DELETE CASCADE ON UPDATE CASCADE;

apps/api/prisma/schema.prisma

@@ -98,10 +98,36 @@ model UserProfile {
   /// a time — but Prisma models the admin side of a one-to-many FK as a
   /// list regardless of that real-world cardinality.
   administeredHouses House[]              @relation("HouseAdmin")
+  preferences        UserPreference?
 
   @@map("user_profiles")
 }
 
+/// Not in the original spec doc — personalization settings (theme for now,
+/// meant to grow), one row per profile, created on demand (see
+/// `preferences.service.ts`) rather than at signup — same "absent means the
+/// default" philosophy as `dietId`/allergies.
+enum ThemePreference {
+  LIGHT
+  DARK
+  /// Follow the OS/browser preference — the default. Not "no row yet" (that
+  /// case is handled in the service layer) but an explicit choice to track
+  /// the system, distinguishable from a user who hasn't decided yet if this
+  /// model ever needs that distinction.
+  SYSTEM
+}
+
+model UserPreference {
+  /// Both the primary key and the FK — a strict 1-1 with UserProfile, no
+  /// separate auto-incrementing id (a profile has at most one preferences row).
+  userProfileId Int             @id @map("user_profile_id")
+  theme         ThemePreference @default(SYSTEM)
+
+  userProfile UserProfile @relation(fields: [userProfileId], references: [id], onDelete: Cascade)
+
+  @@map("user_preference")
+}
+
 /// Explicit join table for the user_profiles <-> allergy association
 /// (documented in the spec as a plain many-to-many, no extra fields).
 model UserProfileAllergy {

packages/shared/src/index.ts

@@ -8,9 +8,11 @@ export * from "./schemas/account.js";
 export * from "./schemas/auth.js";
 export * from "./schemas/household.js";
 export * from "./schemas/planning.js";
+export * from "./schemas/preferences.js";
 export * from "./schemas/profile.js";
 export * from "./tools/assert-is-never.js";
 export * from "./types/household.js";
 export * from "./types/planning.js";
+export * from "./types/preferences.js";
 export * from "./types/reference.js";
 export * from "./types/user-profile.js";

packages/shared/src/schemas/preferences.ts

@@ -0,0 +1,11 @@
+import { z } from "zod";
+import { THEME_PREFERENCES } from "../types/preferences.js";
+
+// See schemas/auth.ts for the shared client/server validation rationale.
+
+/** Payload accepted by `PATCH /preferences`. */
+export const updatePreferencesSchema = z.object({
+  theme: z.enum(THEME_PREFERENCES),
+});
+/** Inferred TS type for {@link updatePreferencesSchema}'s validated output. */
+export type UpdatePreferencesInput = z.infer<typeof updatePreferencesSchema>;

packages/shared/src/types/preferences.ts

@@ -0,0 +1,15 @@
+/**
+ * The 3 values a profile's theme preference can take — `SYSTEM` means "no
+ * explicit choice, follow the OS/browser preference" (see `apps/web`'s
+ * `ThemeContext`, which maps this to *not* setting the `data-theme`
+ * attribute at all, letting `_theme.scss`'s `prefers-color-scheme` media
+ * query take over).
+ */
+export const THEME_PREFERENCES = ["LIGHT", "DARK", "SYSTEM"] as const;
+/** Inferred TS type for one {@link THEME_PREFERENCES} member. */
+export type ThemePreference = (typeof THEME_PREFERENCES)[number];
+
+/** A profile's personalization preferences, as returned by `GET /preferences` / `PATCH /preferences`. */
+export interface PreferencesView {
+  theme: ThemePreference;
+}