feat: add platform marketing homepage with signup flow

Implement complete marketing homepage for Wizamart targeting Letzshop
vendors in Luxembourg. Includes:

- Marketing homepage with hero, pricing tiers, and add-ons
- 4-step signup wizard with Stripe card collection (30-day trial)
- Letzshop vendor lookup for shop claiming
- Platform API endpoints for pricing, vendors, and signup
- Stripe SetupIntent integration for trial with card upfront
- Database fields for Letzshop vendor identity tracking

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/api/main.py

@@ -10,7 +10,7 @@ This module provides:
 
 from fastapi import APIRouter
 
-from app.api.v1 import admin, shop, vendor
+from app.api.v1 import admin, platform, shop, vendor
 from app.api.v1.shared import language, webhooks
 
 api_router = APIRouter()
@@ -36,6 +36,13 @@ api_router.include_router(vendor.router, prefix="/v1/vendor", tags=["vendor"])
 
 api_router.include_router(shop.router, prefix="/v1/shop", tags=["shop"])
 
+# ============================================================================
+# PLATFORM ROUTES (Public marketing and signup)
+# Prefix: /api/v1/platform
+# ============================================================================
+
+api_router.include_router(platform.router, prefix="/v1/platform", tags=["platform"])
+
 # ============================================================================
 # SHARED ROUTES (Cross-context utilities)
 # Prefix: /api/v1