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_response_limits.py

@@ -0,0 +1,46 @@
+"""Tests for response size bounds."""
+
+from __future__ import annotations
+
+import pytest
+
+from aegis_gitea_mcp.config import reset_settings
+from aegis_gitea_mcp.response_limits import ResponseLimitError, limit_items, limit_text
+
+
+def test_limit_items_uses_configured_default(
+    mock_env: None, monkeypatch: pytest.MonkeyPatch
+) -> None:
+    monkeypatch.setenv("MAX_TOOL_RESPONSE_ITEMS", "3")
+    reset_settings()
+    items = [{"i": n} for n in range(5)]
+
+    trimmed, omitted = limit_items(items)
+
+    assert trimmed == items[:3]
+    assert omitted == 2
+
+
+def test_limit_items_within_bound(mock_env: None) -> None:
+    items = [{"i": 1}]
+    assert limit_items(items) == (items, 0)
+    assert limit_items(items, configured_limit=1) == (items, 0)
+    assert limit_items([{"i": 1}, {"i": 2}], configured_limit=1) == ([{"i": 1}], 1)
+
+
+def test_limit_text(mock_env: None) -> None:
+    assert limit_text("abcdef", configured_limit=3) == "abc"
+    assert limit_text("abc", configured_limit=10) == "abc"
+
+
+def test_limit_text_default_from_settings(mock_env: None, monkeypatch: pytest.MonkeyPatch) -> None:
+    monkeypatch.setenv("MAX_TOOL_RESPONSE_CHARS", "5")
+    reset_settings()
+    assert limit_text("abcdefghij") == "abcde"
+
+
+def test_invalid_limits_raise(mock_env: None) -> None:
+    with pytest.raises(ResponseLimitError):
+        limit_items([], configured_limit=-1)
+    with pytest.raises(ResponseLimitError):
+        limit_text("x", configured_limit=-1)