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

scripts/stripe_setup.py

@@ -0,0 +1,77 @@
+"""
+Script de setup Stripe : crée les produits et prix dans Stripe Dashboard.
+Lance avec : python scripts/stripe_setup.py
+"""
+import stripe
+import sys
+
+SK = "sk_test_51SkSHkCKXUJE51jnbEtXZ0nKiTHTa8ohDwLH8fZiDVEx6Ze0g5dg4fGJJgX1VgNHvF93GE3HTramT3oQrCaqOxid00OXTcZlsW"
+stripe.api_key = SK
+
+PLANS = [
+    {"id": "starter", "name": "Wordly Starter", "monthly_eur": 900,  "yearly_eur": 8640},
+    {"id": "pro",     "name": "Wordly Pro",     "monthly_eur": 1900, "yearly_eur": 18240},
+    {"id": "business","name": "Wordly Business","monthly_eur": 4900, "yearly_eur": 47040},
+]
+
+results = {}
+for plan in PLANS:
+    print(f"\n>> Creation produit {plan['name']}...")
+    # Search existing product first
+    existing = stripe.Product.search(query=f"name:'{plan['name']}'", limit=1)
+    if existing.data:
+        product = existing.data[0]
+        print(f"  Produit existant: {product.id}")
+    else:
+        product = stripe.Product.create(
+            name=plan["name"],
+            metadata={"plan_id": plan["id"]}
+        )
+        print(f"  Produit créé: {product.id}")
+
+    # Monthly price
+    monthly_prices = stripe.Price.list(product=product.id, active=True, limit=10)
+    monthly_price = None
+    yearly_price = None
+    for p in monthly_prices.data:
+        if p.recurring and p.recurring.interval == "month" and p.unit_amount == plan["monthly_eur"]:
+            monthly_price = p
+        if p.recurring and p.recurring.interval == "year" and p.unit_amount == plan["yearly_eur"]:
+            yearly_price = p
+
+    if not monthly_price:
+        monthly_price = stripe.Price.create(
+            product=product.id,
+            unit_amount=plan["monthly_eur"],
+            currency="eur",
+            recurring={"interval": "month"},
+            metadata={"plan_id": plan["id"], "billing": "monthly"}
+        )
+        print(f"  Prix mensuel créé: {monthly_price.id}")
+    else:
+        print(f"  Prix mensuel existant: {monthly_price.id}")
+
+    if not yearly_price:
+        yearly_price = stripe.Price.create(
+            product=product.id,
+            unit_amount=plan["yearly_eur"],
+            currency="eur",
+            recurring={"interval": "year"},
+            metadata={"plan_id": plan["id"], "billing": "yearly"}
+        )
+        print(f"  Prix annuel créé: {yearly_price.id}")
+    else:
+        print(f"  Prix annuel existant: {yearly_price.id}")
+
+    results[plan["id"]] = {
+        "monthly": monthly_price.id,
+        "yearly": yearly_price.id,
+    }
+
+print("\n" + "="*60)
+print("Variables à ajouter dans .env.production et .env :")
+print("="*60)
+for plan_id, ids in results.items():
+    print(f"STRIPE_PRICE_{plan_id.upper()}_MONTHLY={ids['monthly']}")
+    print(f"STRIPE_PRICE_{plan_id.upper()}_YEARLY={ids['yearly']}")
+print("="*60)