FAS 1b: Progressive onboarding (3-layer flow)

- Add PROGRESSIVE_ONBOARDING feature flag to KNOWN_FLAGS
- Add onboarding_step column to users table (a/b/c)
- New backend endpoints:
  - GET /v1/onboarding/status – check current step + feature flag
  - POST /v1/onboarding/quick-start – complete Step A (goal + precision)
  - POST /v1/onboarding/complete-b – complete Step B (diet, allergens, household)
  - POST /v1/onboarding/complete-c – complete Step C (health profile)
  - POST /v1/onboarding/skip – GDPR-friendly skip
- Refactor mobile onboarding screen into 3 progressive layers
- Update auth store with onboardingStep state
- Update tab layout to only block on Step A
- Update registration to set onboardingStep='a'
- Add i18n keys for Step B/C titles across all 12 locales
- Add Zod validation schemas (quickStartInputSchema, onboardingStatusSchema)
- Add tests for validation and feature flag
- Preserve existing /v1/me/onboarding for backward compatibility
- Migration: 0004_progressive_onboarding.sql

packages/feature-flags/src/index.ts

@@ -19,6 +19,7 @@ export const KNOWN_FLAGS = {
   FOOD_MEMORIES: "food_memories",
   VOICE_INPUT: "voice_input",
   AI_RERANK: "ai_rerank",
+  PROGRESSIVE_ONBOARDING: "progressive_onboarding",
 } as const;
 export type KnownFlagKey = (typeof KNOWN_FLAGS)[keyof typeof KNOWN_FLAGS];