feat: Stripe integration complete - products created, DB migration, payment_failed handler, credit buttons wired

- Create Stripe products/prices (Starter/Pro/Business monthly+yearly)
- Fix CRITICAL bug: add subscription_ends_at + cancel_at_period_end columns to users table
- Alembic migration: f6a7b8c9d0e1_add_subscription_ends_at_cancel_at_period_end
- Fix: implement handle_payment_failed() to set subscription_status=PAST_DUE
- Fix: harmonize .env.production Stripe variable names to match pricing_config.py
- Fix: add missing FRONTEND_URL and STRIPE_PUBLISHABLE_KEY to .env.production
- Add all Stripe Price IDs (test mode) to .env.production
- Wire credit purchase buttons to /api/v1/auth/create-credits-checkout
- Dashboard sync post-checkout was already implemented (no change needed)

Stripe test keys: configured in .env.production
Webhook: must be configured on server via stripe CLI or Stripe Dashboard
Webhook URL: https://wordly.art/api/v1/auth/webhook/stripe

services/payment_service.py

@@ -2,9 +2,12 @@
 Stripe payment integration for subscriptions and credits
 """
 import os
+import logging
 from typing import Optional, Dict, Any
 from datetime import datetime
 
+logger = logging.getLogger(__name__)
+
 # Try to import stripe
 try:
     import stripe
@@ -347,13 +350,33 @@ async def handle_subscription_deleted(subscription: Dict):
 
 
 async def handle_payment_failed(invoice: Dict):
-    """Handle failed payment"""
+    """Handle failed payment — set subscription status to PAST_DUE"""
     customer_id = invoice.get("customer")
     if not customer_id:
         return
-    
-    # Find user by customer ID and update status
-    # In production, query database by stripe_customer_id
+
+    # Find user by stripe_customer_id
+    user = None
+    try:
+        from database.connection import get_sync_session
+        from database.models import User as DBUser
+
+        with get_sync_session() as session:
+            db_user = (
+                session.query(DBUser)
+                .filter(DBUser.stripe_customer_id == customer_id)
+                .first()
+            )
+            if db_user:
+                user_id = str(db_user.id)
+                db_user.subscription_status = SubscriptionStatus.PAST_DUE
+                session.commit()
+                logger.warning(
+                    "Payment failed for customer %s (user %s) — status set to past_due",
+                    customer_id, user_id,
+                )
+    except Exception as exc:
+        logger.error("handle_payment_failed DB error: %s", exc)
 
 
 async def cancel_subscription(user_id: str) -> Dict[str, Any]: