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_commits.py

@@ -0,0 +1,94 @@
+import pytest
+import httpx
+import respx
+from server.gitea_mcp import list_commits, get_commit, compare_branches, list_repo_contributors
+
+BASE = "https://gitea.test/api/v1"
+
+
+@respx.mock
+def test_list_commits_defaults():
+    route = respx.get(f"{BASE}/repos/owner/repo/commits").mock(
+        return_value=httpx.Response(200, json=[{"sha": "abc123"}])
+    )
+    result = list_commits("owner", "repo")
+    assert route.called
+    params = dict(route.calls[0].request.url.params)
+    assert params["limit"] == "20"
+    assert params["page"] == "1"
+    assert "sha" not in params
+    assert "path" not in params
+
+
+@respx.mock
+def test_list_commits_on_branch_and_path():
+    route = respx.get(f"{BASE}/repos/owner/repo/commits").mock(
+        return_value=httpx.Response(200, json=[])
+    )
+    list_commits("owner", "repo", sha="develop", path="server/gitea_mcp.py")
+    params = dict(route.calls[0].request.url.params)
+    assert params["sha"] == "develop"
+    assert params["path"] == "server/gitea_mcp.py"
+
+
+@respx.mock
+def test_get_commit():
+    route = respx.get(f"{BASE}/repos/owner/repo/git/commits/abc123").mock(
+        return_value=httpx.Response(200, json={"sha": "abc123", "commit": {"message": "fix bug"}})
+    )
+    result = get_commit("owner", "repo", "abc123")
+    assert route.called
+    assert result["sha"] == "abc123"
+    params = dict(route.calls[0].request.url.params)
+    assert params["stat"] == "true"
+    assert params["files"] == "true"
+
+
+@respx.mock
+def test_get_commit_without_stat():
+    route = respx.get(f"{BASE}/repos/owner/repo/git/commits/deadbeef").mock(
+        return_value=httpx.Response(200, json={"sha": "deadbeef"})
+    )
+    get_commit("owner", "repo", "deadbeef", stat=False, files=False)
+    params = dict(route.calls[0].request.url.params)
+    assert params["stat"] == "false"
+    assert params["files"] == "false"
+
+
+@respx.mock
+def test_get_commit_not_found():
+    respx.get(f"{BASE}/repos/owner/repo/git/commits/notacommit").mock(
+        return_value=httpx.Response(404, json={"message": "not found"})
+    )
+    with pytest.raises(RuntimeError, match="404"):
+        get_commit("owner", "repo", "notacommit")
+
+
+@respx.mock
+def test_compare_branches():
+    route = respx.get(f"{BASE}/repos/owner/repo/compare/main...develop").mock(
+        return_value=httpx.Response(200, json={"total_commits": 3, "commits": []})
+    )
+    result = compare_branches("owner", "repo", "main", "develop")
+    assert route.called
+    assert result["total_commits"] == 3
+
+
+@respx.mock
+def test_compare_branches_with_slashes():
+    route = respx.get(f"{BASE}/repos/owner/repo/compare/release%2F1.0...feature%2Fnew").mock(
+        return_value=httpx.Response(200, json={"total_commits": 1})
+    )
+    result = compare_branches("owner", "repo", "release/1.0", "feature/new")
+    assert route.called
+
+
+@respx.mock
+def test_list_repo_contributors():
+    route = respx.get(f"{BASE}/repos/owner/repo/contributors").mock(
+        return_value=httpx.Response(200, json=[{"login": "alice", "contributions": 42}])
+    )
+    result = list_repo_contributors("owner", "repo")
+    assert route.called
+    assert result[0]["login"] == "alice"
+    assert dict(route.calls[0].request.url.params)["limit"] == "20"