feat: Implement automatic git repository configuration detection for Gitea

- Add GiteaConfig.from_git_repository() method for auto-detection
- Support HTTP(S) and SSH git remote URL formats
- Parse gitea_url, repo_owner, repo_name from git remote origin
- Only requires GITEA_API_TOKEN environment variable
- Update GiteaClient to use auto-detection as primary method
- Maintain backward compatibility with environment variables
- Fix issue creation API to use label IDs instead of names
- Add comprehensive error handling and validation
- Successfully tested with issues #33 and #34

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

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

gitea/client.py

@@ -170,10 +170,14 @@ class GiteaClient:
         """Initialize Gitea client.
 
         Args:
-            config: GiteaConfig instance. If None, loads from environment.
+            config: GiteaConfig instance. If None, auto-detects from git repository.
         """
         if config is None:
-            config = GiteaConfig.from_environment()
+            try:
+                config = GiteaConfig.from_git_repository()
+            except Exception:
+                # Fallback to environment-based config if git detection fails
+                config = GiteaConfig.from_environment()
             config.validate()
 
         self.config = config