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.

tests/test_request_context.py

@@ -0,0 +1,35 @@
+"""Tests for request-scoped context variables."""
+
+from __future__ import annotations
+
+from aegis_gitea_mcp.request_context import (
+    clear_gitea_auth_context,
+    get_gitea_user_login,
+    get_gitea_user_scopes,
+    get_gitea_user_token,
+    get_request_id,
+    set_gitea_user_login,
+    set_gitea_user_scopes,
+    set_gitea_user_token,
+    set_request_id,
+)
+
+
+def test_request_id_roundtrip() -> None:
+    set_request_id("req-1")
+    assert get_request_id() == "req-1"
+
+
+def test_auth_context_set_and_clear() -> None:
+    set_gitea_user_token("tok")
+    set_gitea_user_login("alice")
+    set_gitea_user_scopes([" write:repository", "read:user", "read:user", ""])
+
+    assert get_gitea_user_token() == "tok"
+    assert get_gitea_user_login() == "alice"
+    assert get_gitea_user_scopes() == ("read:user", "write:repository")
+
+    clear_gitea_auth_context()
+    assert get_gitea_user_token() is None
+    assert get_gitea_user_login() is None
+    assert get_gitea_user_scopes() == ()