feat: new settings, CLI skeleton and interface skeletons

Adds the pydantic-settings Settings with validated GITEA_URL, OAuth scopes
and toolsets, the argparse CLI skeleton, catalog.model, identity and
GiteaAPIError. Test fixtures now isolate env, cwd and state paths in tmp.

src/aegis_gitea_mcp/__init__.py

@@ -1,3 +1,3 @@
 """AegisGitea MCP - Security-first MCP gateway for self-hosted Gitea."""
 
-__version__ = "0.2.0"
+__version__ = "1.0.0.dev0"