feat(marketplace): Add Crawl4AI marketplace with secure configuration

- Implement marketplace frontend and admin dashboard
- Add FastAPI backend with environment-based configuration
- Use .env file for secrets management
- Include data generation scripts
- Add proper CORS configuration
- Remove hardcoded password from admin login
- Update gitignore for security

docs/md_v2/marketplace/backend/.env.example

@@ -0,0 +1,14 @@
+# Marketplace Configuration
+# Copy this to .env and update with your values
+
+# Admin password (required)
+MARKETPLACE_ADMIN_PASSWORD=change_this_password
+
+# JWT secret key (required) - generate with: python3 -c "import secrets; print(secrets.token_urlsafe(32))"
+MARKETPLACE_JWT_SECRET=change_this_to_a_secure_random_key
+
+# Database path (optional, defaults to ./marketplace.db)
+MARKETPLACE_DB_PATH=./marketplace.db
+
+# Token expiry in hours (optional, defaults to 4)
+MARKETPLACE_TOKEN_EXPIRY=4