feat: Add Gitea release cleanup executor

- Add gitea_release_cleanup_executor for automated release cleanup
- Add GITEA_TOKEN setting for API token authentication
- Configurable retention count, repo exclusions, and dry-run mode
- Designed to run daily before Watchtower (3 AM)

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

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

src/config.py

@@ -57,6 +57,7 @@ class Settings(BaseSettings):
     gitea_url: str = Field(default="http://gitea:3000", alias="GITEA_URL")
     gitea_user: str = Field(default="library", alias="GITEA_USER")
     gitea_password: str = Field(default="", alias="GITEA_PASSWORD")
+    gitea_token: str = Field(default="", alias="GITEA_TOKEN")  # API token with write:repository scope
     gitea_ssh_host: str = Field(default="gitea", alias="GITEA_SSH_HOST")
     gitea_ssh_port: int = Field(default=22, alias="GITEA_SSH_PORT")