feat: implement OpenAPI auto-discovery system

[iacapuca]

Implement a self-discovery system for OpenAPI spec generation that eliminates manual registration of API apps.

Changes:

• Add scripts/generate-all-openapi.ts for automatic app discovery
• Update root package.json to use discovery script
• Remove generate-openapi from individual app build scripts
• Add comprehensive documentation in docs/OPENAPI_DISCOVERY.md
• Update README.md with auto-discovery information
• Add tsx as dev dependency for running discovery script

Discovery Criteria:
Apps are automatically discovered if they have:

1. A 'generate-openapi' script in package.json
2. A src/generate-openapi.ts file

Benefits:

• Zero configuration - new apps are automatically discovered
• No manual registration in any central file
• Consistent behavior across all API services
• Single command (pnpm generate-openapi) generates all specs
• Specs are automatically copied to docs app

Example Output:
🔍 Discovering apps with OpenAPI generation capability...

Found 3 app(s) with OpenAPI generation: ✓ cyclist-counts (@atlas/cyclist-counts) ✓ cyclist-profile (@atlas/cyclist-profile) ✓ traffic-deaths (@atlas/traffic-deaths)

🎉 All OpenAPI specs generated successfully!

This is the first step in implementing self-discovery patterns across the monorepo to reduce manual configuration and improve developer experience.