feat(checkout): add POST /create-checkout-session endpoint

Delegates to existing /v1/keys/setup handler for Stripe Checkout Session
creation. Accessible at /create-checkout-session for pricing page CTAs.
Also added to failover blocked paths for split-brain protection.

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

Author: desiorac

trust_layer/app.py

@@ -54,6 +54,7 @@ def _is_failover_mode() -> bool:
     "/v1/compliance-report",
     "/v1/contact",
     "/v1/track/event",
+    "/create-checkout-session",
 }
 
 
@@ -1023,6 +1024,19 @@ async def setup_key(request: Request):
         return _error_response("internal_error", f"Stripe error: {str(e)}", 500)
 
 
+# --- POST /create-checkout-session (pricing page standard checkout) ---
+
+@app.post("/create-checkout-session")
+async def create_checkout_session(request: Request):
+    """Standard Stripe Checkout Session endpoint for pricing page CTAs.
+
+    Delegates to the full /v1/keys/setup handler which creates a Stripe
+    Checkout Session (subscription mode, 14-day trial, Pro at 29 EUR/month).
+    Returns {checkout_url, session_id, customer_id, mode, plan, price_monthly_eur, proofs_per_month}.
+    """
+    return await setup_key(request)
+
+
 # --- GET /trial (landing page for README/CLI badge links) ---
 
 @app.get("/trial")