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/core/config.py

@@ -217,6 +217,12 @@ class Settings(BaseSettings):
     # =============================================================================
     cloudflare_enabled: bool = False  # Set to True when using CloudFlare proxy
 
+    # =============================================================================
+    # GOOGLE WALLET (LOYALTY MODULE)
+    # =============================================================================
+    loyalty_google_issuer_id: str | None = None
+    loyalty_google_service_account_json: str | None = None  # Path to service account JSON
+
     model_config = {"env_file": ".env"}