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/wallet_service.py

@@ -47,8 +47,8 @@ class WalletService:
 
         program = card.program
 
-        # Google Wallet
-        if program.google_issuer_id or program.google_class_id:
+        # Google Wallet — platform-wide config via env vars
+        if google_wallet_service.is_configured or program.google_class_id:
             try:
                 urls["google_wallet_url"] = google_wallet_service.get_save_url(db, card)
             except Exception as e:  # noqa: EXC003
@@ -131,8 +131,8 @@ class WalletService:
 
         program = card.program
 
-        # Create Google Wallet object
-        if program.google_issuer_id:
+        # Create Google Wallet object — platform-wide config via env vars
+        if google_wallet_service.is_configured:
             try:
                 google_wallet_service.create_object(db, card)
                 results["google_wallet"] = True