feat(db): encrypt Profile health fields at rest (ADR 0002)

Wire prisma-field-encryption AES-256-GCM extension on the shared Prisma
client and annotate the four sensitive columns on Profile with @encrypted:
- weightStartKg / weightCurrentKg / weightGoalKg (Decimal → String)
- targetDate (DateTime @db.Date → String, ISO YYYY-MM-DD)

Other Profile fields stay in clear text per ADR 0002 (age, gender,
heightCm, activityLevel) — they're needed for plan generation and
aggregate analytics, and are not strongly identifying on their own.

apps/api profile.routes.ts:
- serialize() now reads the columns as strings and parses them back to
  numbers for BMR/TDEE; targetDate is already an ISO string from the DB
- the upsert stringifies numeric inputs and slices the date to YYYY-MM-DD

Env wiring:
- packages/db, apps/api, apps/web .env.example all document
  PRISMA_FIELD_ENCRYPTION_KEY (k1.aesgcm256.<base64url>) — must match
  across every process that hits the DB
- key generation snippet documented inline

Migration is intentionally NOT in this commit: needs to be created against
a live Postgres instance and applied. The fields change Decimal/Date → text
so prisma migrate dev will require a USING cast — see the follow-up commit.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/db/.env.example

@@ -1 +1,4 @@
 DATABASE_URL="postgresql://luciano:luciano%40@localhost:5432/ketopath?schema=public"
+
+# Cifratura at-rest (vedi ADR 0002). Stesso valore in apps/api/.env e apps/web/.env.
+PRISMA_FIELD_ENCRYPTION_KEY=

packages/db/package.json

@@ -19,7 +19,8 @@
     "db:seed": "tsx prisma/seed.ts"
   },
   "dependencies": {
-    "@prisma/client": "^5.18.0"
+    "@prisma/client": "^5.18.0",
+    "prisma-field-encryption": "^1.6.0"
   },
   "devDependencies": {
     "@ketopath/eslint-config": "workspace:*",

packages/db/prisma/schema.prisma

@@ -128,11 +128,15 @@ model Profile {
   age             Int
   gender          Gender
   heightCm        Int           @map("height_cm")
-  weightStartKg   Decimal       @map("weight_start_kg") @db.Decimal(5, 2)
-  weightCurrentKg Decimal       @map("weight_current_kg") @db.Decimal(5, 2)
-  weightGoalKg    Decimal       @map("weight_goal_kg") @db.Decimal(5, 2)
+  /// @encrypted
+  weightStartKg   String        @map("weight_start_kg")
+  /// @encrypted
+  weightCurrentKg String        @map("weight_current_kg")
+  /// @encrypted
+  weightGoalKg    String        @map("weight_goal_kg")
   activityLevel   ActivityLevel @map("activity_level")
-  targetDate      DateTime?     @map("target_date") @db.Date
+  /// @encrypted
+  targetDate      String?       @map("target_date")
   currentPhase    Phase         @default(INTENSIVE) @map("current_phase")
   createdAt       DateTime      @default(now()) @map("created_at")
   updatedAt       DateTime      @updatedAt @map("updated_at")

packages/db/src/client.ts

@@ -1,13 +1,19 @@
 import { PrismaClient } from '@prisma/client';
+import { fieldEncryptionExtension } from 'prisma-field-encryption';
 
+// Singleton-friendly storage of the BASE client (so HMR doesn't open a new pool
+// every time). The exported `prisma` is the EXTENDED client returned by
+// $extends — it wraps the base client with the field-encryption middleware.
 const globalForPrisma = globalThis as unknown as { prisma?: PrismaClient };
 
-export const prisma: PrismaClient =
+const baseClient =
   globalForPrisma.prisma ??
   new PrismaClient({
     log: process.env.NODE_ENV === 'development' ? ['warn', 'error'] : ['error'],
   });
 
 if (process.env.NODE_ENV !== 'production') {
-  globalForPrisma.prisma = prisma;
+  globalForPrisma.prisma = baseClient;
 }
+
+export const prisma = baseClient.$extends(fieldEncryptionExtension());