feat(v1.2.0): retry API, dernier commit, tri, coloration, export JSON

- client.py: _get_with_retry (max 2 retries, backoff lineaire), get_latest_commit
- collector.py: champ last_commit_date dans RepoData
- display.py: colonne "Dernier commit", _sort_repos (name/issues/release/activity),
  _colorize_milestone_due (rouge/jaune/vert selon echeance)
- cli.py: options --sort/-s et --format/-f (table/json)
- exporter.py: nouveau module, repos_to_dicts + export_json
- 88 tests (35 nouveaux), ruff clean

fixes #8, fixes #7, fixes #10, fixes #9, fixes #6

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/test_client.py

@@ -2,6 +2,8 @@
 
 from unittest.mock import MagicMock, patch
 
+import pytest
+import requests
 
 from gitea_dashboard.client import GiteaClient
 
@@ -129,7 +131,6 @@ class TestGetLatestRelease:
 
     def test_raises_on_server_error(self):
         """HTTP 500 raises an exception instead of silently returning bad data."""
-        import pytest
         import requests as req
 
         client = GiteaClient("http://gitea.local:3000", "tok")
@@ -158,3 +159,92 @@ class TestGetMilestones:
             params={"state": "open"},
         )
         assert result == milestones
+
+
+class TestGetWithRetry:
+    """Test _get_with_retry method (retry on timeout)."""
+
+    def _make_client(self):
+        return GiteaClient("http://gitea.local:3000", "tok")
+
+    @patch("time.sleep")
+    def test_success_first_attempt(self, mock_sleep):
+        """No timeout — returns response directly without sleeping."""
+        client = self._make_client()
+        mock_resp = MagicMock()
+
+        with patch.object(client.session, "get", return_value=mock_resp):
+            result = client._get_with_retry("http://gitea.local:3000/api/v1/test")
+
+        assert result is mock_resp
+        mock_sleep.assert_not_called()
+
+    @patch("time.sleep")
+    def test_success_after_timeout(self, mock_sleep):
+        """First call times out, second succeeds — one sleep of 1.0s."""
+        client = self._make_client()
+        mock_resp = MagicMock()
+
+        with patch.object(
+            client.session, "get", side_effect=[requests.Timeout("timeout"), mock_resp]
+        ):
+            result = client._get_with_retry("http://gitea.local:3000/api/v1/test")
+
+        assert result is mock_resp
+        mock_sleep.assert_called_once_with(1.0)
+
+    @patch("time.sleep")
+    def test_all_timeouts(self, mock_sleep):
+        """All 3 attempts timeout — raises Timeout, sleeps twice (1.0, 2.0)."""
+        client = self._make_client()
+        timeout_exc = requests.Timeout("timeout")
+
+        with patch.object(
+            client.session, "get", side_effect=[timeout_exc, timeout_exc, timeout_exc]
+        ):
+            with pytest.raises(requests.Timeout):
+                client._get_with_retry("http://gitea.local:3000/api/v1/test")
+
+        assert mock_sleep.call_count == 2
+        mock_sleep.assert_any_call(1.0)
+        mock_sleep.assert_any_call(2.0)
+
+
+class TestGetLatestCommit:
+    """Test get_latest_commit method."""
+
+    def test_returns_first_commit(self):
+        """Returns the first commit from the list."""
+        client = GiteaClient("http://gitea.local:3000", "tok")
+        commit = {"sha": "abc123", "created": "2026-03-10T14:30:00Z"}
+        mock_resp = MagicMock()
+        mock_resp.status_code = 200
+        mock_resp.json.return_value = [commit]
+
+        with patch.object(client.session, "get", return_value=mock_resp):
+            result = client.get_latest_commit("admin", "my-repo")
+
+        assert result == commit
+
+    def test_empty_repo_returns_none(self):
+        """Returns None when repo has no commits."""
+        client = GiteaClient("http://gitea.local:3000", "tok")
+        mock_resp = MagicMock()
+        mock_resp.status_code = 200
+        mock_resp.json.return_value = []
+
+        with patch.object(client.session, "get", return_value=mock_resp):
+            result = client.get_latest_commit("admin", "empty-repo")
+
+        assert result is None
+
+    def test_404_returns_none(self):
+        """Returns None when repo is not found (404)."""
+        client = GiteaClient("http://gitea.local:3000", "tok")
+        mock_resp = MagicMock()
+        mock_resp.status_code = 404
+
+        with patch.object(client.session, "get", return_value=mock_resp):
+            result = client.get_latest_commit("admin", "missing-repo")
+
+        assert result is None