feat(loyalty): Phase 1 production launch hardening

Phase 1 of the loyalty production launch plan: config & security
hardening, dropped-data fix, DB integrity guards, rate limiting, and
constant-time auth compare. 362 tests pass.

- 1.4 Persist customer birth_date (new column + migration). Enrollment
  form was collecting it but the value was silently dropped because
  create_customer_for_enrollment never received it. Backfills existing
  customers without overwriting.
- 1.1 LOYALTY_GOOGLE_SERVICE_ACCOUNT_JSON validated at startup (file
  must exist and be readable; ~ expanded). Adds is_google_wallet_enabled
  and is_apple_wallet_enabled derived flags. Prod path documented as
  ~/apps/orion/google-wallet-sa.json.
- 1.5 CHECK constraints on loyalty_cards (points_balance, stamp_count
  non-negative) and loyalty_programs (min_purchase, points_per_euro,
  welcome_bonus non-negative; stamps_target >= 1). Mirrored as
  CheckConstraint in models. Pre-flight scan showed zero violations.
- 1.3 @rate_limit on store mutating endpoints: stamp 60/min,
  redeem/points-earn 30-60/min, void/adjust 20/min, pin unlock 10/min.
- 1.2 Constant-time hmac.compare_digest for Apple Wallet auth token
  (pulled forward from Phase 9 — code is safe whenever Apple ships).

See app/modules/loyalty/docs/production-launch-plan.md for the full
launch plan and remaining phases.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

app/modules/customers/services/customer_service.py

@@ -7,7 +7,7 @@ with complete store isolation.
 """
 
 import logging
-from datetime import UTC, datetime, timedelta
+from datetime import UTC, date, datetime, timedelta
 from typing import Any
 
 from sqlalchemy import and_
@@ -567,6 +567,7 @@ class CustomerService:
         first_name: str = "",
         last_name: str = "",
         phone: str | None = None,
+        birth_date: date | None = None,
     ) -> Customer:
         """
         Create a customer for loyalty/external enrollment.
@@ -580,6 +581,7 @@ class CustomerService:
             first_name: First name
             last_name: Last name
             phone: Phone number
+            birth_date: Date of birth (optional)
 
         Returns:
             Created Customer object
@@ -603,6 +605,7 @@ class CustomerService:
             first_name=first_name,
             last_name=last_name,
             phone=phone,
+            birth_date=birth_date,
             hashed_password=unusable_hash,
             customer_number=cust_number,
             store_id=store_id,