feat: Add subdomain mode to URLs scan and fix GitHub Actions workflows

- Added --subdomain flag to URLs scan command (CLI, Discord, API)
- URLs scan now supports single subdomain mode (skips subdomain enumeration)
- Updated external API calls to work with subdomains directly
- Fixed GitHub Actions workflows to handle submodule checkout failures gracefully
- Added Discord Guild ID (GUID) configuration via .env file (DISCORD_ALLOWED_GUILD_ID)
- Added /docs endpoint with comprehensive API documentation
- Updated urlfinder tool to support subdomain mode
- All modules updated to use new CollectURLs signature (backward compatible)

Author: h0tak88r