feat: add MCP server + shared auth module (#7, #1)

- New: mcp_server.py — FastMCP stdio server exposing 7 tools:
  gitea_create_issue, gitea_create_pr, gitea_close_issue,
  gitea_list_issues, gitea_view_issue, gitea_mark_issue,
  gitea_mirror_refs
- New: auth.py — shared authentication and API helpers
  (get_credentials, get_auth_header, api_request, repo_api_url)
- Refactored: create_pr.py, create_issue.py, manage_labels.py
  to use shared auth module (eliminates credential duplication)
- New: tests/test_mcp_server.py — 17 tests for all MCP tools
- Updated: tests/test_credentials.py — now tests auth.py directly
- Updated: tests/test_create_issue.py — adapted for refactored imports
- New: requirements.txt — frozen venv deps (mcp[cli], pytest)
- Updated: README.md — MCP server as primary interface
- Config: added gitea-tools to mcp_config.json

Closes #1. Resolves #2, #5. Relates to #7.

tests/test_credentials.py

@@ -1,4 +1,4 @@
-"""Tests for the shared get_credentials() function used by create_issue.py and create_pr.py.
+"""Tests for the shared get_credentials() function in auth.py.
 
 These test the credential parsing logic in isolation by mocking subprocess.Popen.
 """
@@ -7,7 +7,7 @@ import unittest
 from unittest.mock import MagicMock, patch
 
 sys.path.insert(0, str(__import__("pathlib").Path(__file__).resolve().parent.parent))
-import create_pr  # noqa: E402  (get_credentials is identical in create_issue.py and create_pr.py)
+import auth  # noqa: E402
 
 
 class TestGetCredentials(unittest.TestCase):
@@ -19,45 +19,45 @@ class TestGetCredentials(unittest.TestCase):
         mock_proc.communicate.return_value = (output_text, "")
         return mock_proc
 
-    @patch("create_pr.subprocess.Popen")
+    @patch("auth.subprocess.Popen")
     def test_parses_standard_output(self, mock_popen_cls):
         mock_popen_cls.return_value = self._mock_popen(
             "protocol=https\nhost=gitea.example.com\nusername=admin\npassword=s3cret\n"
         )
-        user, password = create_pr.get_credentials("gitea.example.com")
+        user, password = auth.get_credentials("gitea.example.com")
         self.assertEqual(user, "admin")
         self.assertEqual(password, "s3cret")
 
-    @patch("create_pr.subprocess.Popen")
+    @patch("auth.subprocess.Popen")
     def test_handles_password_with_equals(self, mock_popen_cls):
         # Tokens often contain '=' characters
         mock_popen_cls.return_value = self._mock_popen(
             "username=bot\npassword=abc=def=ghi\n"
         )
-        user, password = create_pr.get_credentials("example.com")
+        user, password = auth.get_credentials("example.com")
         self.assertEqual(user, "bot")
         self.assertEqual(password, "abc=def=ghi")
 
-    @patch("create_pr.subprocess.Popen")
+    @patch("auth.subprocess.Popen")
     def test_empty_output_returns_empty(self, mock_popen_cls):
         mock_popen_cls.return_value = self._mock_popen("")
-        user, password = create_pr.get_credentials("example.com")
+        user, password = auth.get_credentials("example.com")
         self.assertEqual(user, "")
         self.assertEqual(password, "")
 
-    @patch("create_pr.subprocess.Popen")
+    @patch("auth.subprocess.Popen")
     def test_missing_password_returns_empty(self, mock_popen_cls):
         mock_popen_cls.return_value = self._mock_popen("username=admin\n")
-        user, password = create_pr.get_credentials("example.com")
+        user, password = auth.get_credentials("example.com")
         self.assertEqual(user, "admin")
         self.assertEqual(password, "")
 
-    @patch("create_pr.subprocess.Popen")
+    @patch("auth.subprocess.Popen")
     def test_sends_correct_stdin(self, mock_popen_cls):
         mock_proc = self._mock_popen("username=u\npassword=p\n")
         mock_popen_cls.return_value = mock_proc
 
-        create_pr.get_credentials("gitea.prgs.cc")
+        auth.get_credentials("gitea.prgs.cc")
 
         # Verify the correct input was sent to git credential fill
         mock_proc.communicate.assert_called_once_with(
@@ -65,5 +65,27 @@ class TestGetCredentials(unittest.TestCase):
         )
 
 
+class TestGetAuthHeader(unittest.TestCase):
+    """Test the get_auth_header function."""
+
+    @patch("auth.get_credentials", return_value=("user", "pass"))
+    def test_returns_basic_header(self, _cred):
+        header = auth.get_auth_header("example.com")
+        self.assertIsNotNone(header)
+        self.assertTrue(header.startswith("Basic "))
+
+    @patch("auth.get_credentials", return_value=("", ""))
+    def test_returns_none_for_missing_creds(self, _cred):
+        header = auth.get_auth_header("example.com")
+        self.assertIsNone(header)
+
+
+class TestRepoApiUrl(unittest.TestCase):
+
+    def test_url_format(self):
+        url = auth.repo_api_url("gitea.prgs.cc", "Org", "Repo")
+        self.assertEqual(url, "https://gitea.prgs.cc/api/v1/repos/Org/Repo")
+
+
 if __name__ == "__main__":
     unittest.main()