feat: wire Google Wallet into loyalty enrollment, stamps, and points flows

Connect the fully-implemented Google Wallet service to the loyalty module:
- Create wallet class/object on customer enrollment
- Sync wallet passes on stamp and points operations
- Expose wallet URLs in storefront API responses
- Add conditional "Add to Google Wallet" buttons on dashboard and enroll-success pages
- Use platform-wide env var config (not per-merchant DB column)
- Add Google service account patterns to .gitignore
- Add LOYALTY_GOOGLE_* fields to app Settings
- Update deployment docs and add local testing guide

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/modules/loyalty/services/stamp_service.py

@@ -154,6 +154,11 @@ class StampService:
         db.commit()
         db.refresh(card)
 
+        # Sync wallet passes with updated stamp count
+        from app.modules.loyalty.services.wallet_service import wallet_service
+
+        wallet_service.sync_card_to_wallets(db, card)
+
         stamps_today += 1
 
         logger.info(
@@ -273,6 +278,11 @@ class StampService:
         db.commit()
         db.refresh(card)
 
+        # Sync wallet passes with updated stamp count
+        from app.modules.loyalty.services.wallet_service import wallet_service
+
+        wallet_service.sync_card_to_wallets(db, card)
+
         logger.info(
             f"Redeemed stamps from card {card.id} at store {store_id} "
             f"(reward: {program.stamps_reward_description}, "
@@ -400,6 +410,11 @@ class StampService:
         db.commit()
         db.refresh(card)
 
+        # Sync wallet passes with updated stamp count
+        from app.modules.loyalty.services.wallet_service import wallet_service
+
+        wallet_service.sync_card_to_wallets(db, card)
+
         logger.info(
             f"Voided {actual_voided} stamps from card {card.id} at store {store_id} "
             f"(balance: {card.stamp_count})"