Fix Docker Compose configuration issues

[raphael-solace]

This commit addresses multiple issues in the Docker Compose configuration:

1. Fix YAML parsing error in compose.database.yml

   • Removed duplicate PLATFORM_DATABASE_URL environment variable
   • Database URLs are already defined in base compose.yml and .env file
   • Removed duplicate database initialization in init.sql

2. Fix broker-init idempotency in compose.broker.yml

   • Added check to verify if 'client' user exists before creation
   • Prevents exit 22 error when user already exists
   • Makes broker-init container idempotent and safe to restart

3. Fix platform service module error in compose.yml

   • Removed platform.yaml from SAM container command
   • SAM 1.14.9 image does not include platform service module
   • Prevents ModuleNotFoundError on startup

4. Fix platform database configuration warning in compose.yml

   • Added platform_service.database_url to webui_backend.yml config
   • Enables platform features and removes warning message
   • Allows deployment status tracking and other platform features

These changes ensure the SAM stack starts successfully without errors or warnings.