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

pyproject.toml

@@ -8,5 +8,15 @@ dependencies = [
     "httpx>=0.27",
 ]
 
+[dependency-groups]
+dev = [
+    "pytest>=8.0",
+    "respx>=0.21",
+    "pytest-cov>=5.0",
+]
+
+[tool.pytest.ini_options]
+testpaths = ["tests"]
+
 [tool.uv]
 package = false