test: add 106 unit + smoke tests, 93% coverage

- pytest + respx + pytest-cov added as dev dependencies
- tests/smoke/test_registration.py: verify all 66 tools registered and unique
- tests/unit/: 12 files covering every tool — HTTP method, URL, params/body, errors
- tests/config.test.json + conftest.py: zero-network test setup via GITEA_CONFIG
- CLAUDE.md: developer guide with testing philosophy, pyramid, and commands
- server/gitea_mcp.py: get_commit, list_pr_files tools added
- README.md: tool count corrected to 66

tests/unit/test_meta.py

@@ -0,0 +1,46 @@
+import pytest
+import httpx
+import respx
+from server.gitea_mcp import list_instances, get_server_info, get_current_user
+
+BASE = "https://gitea.test/api/v1"
+
+
+def test_list_instances():
+    result = list_instances()
+    assert result["default"] == "default"
+    assert "default" in result["instances"]
+
+
+@respx.mock
+def test_get_server_info():
+    route = respx.get(f"{BASE}/version").mock(
+        return_value=httpx.Response(200, json={"version": "1.22.0"})
+    )
+    result = get_server_info()
+    assert route.called
+    assert result == {"version": "1.22.0"}
+
+
+@respx.mock
+def test_get_server_info_error():
+    respx.get(f"{BASE}/version").mock(return_value=httpx.Response(500, json={"message": "internal error"}))
+    with pytest.raises(RuntimeError, match="500"):
+        get_server_info()
+
+
+@respx.mock
+def test_get_current_user():
+    route = respx.get(f"{BASE}/user").mock(
+        return_value=httpx.Response(200, json={"login": "alice", "id": 1})
+    )
+    result = get_current_user()
+    assert route.called
+    assert result["login"] == "alice"
+
+
+@respx.mock
+def test_get_current_user_error():
+    respx.get(f"{BASE}/user").mock(return_value=httpx.Response(401, json={"message": "unauthorized"}))
+    with pytest.raises(RuntimeError, match="401"):
+        get_current_user()