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_cli.py

@@ -26,7 +26,7 @@ class TestMainNominal:
 
         mock_client_cls.assert_called_once_with("http://localhost:3000", "test-token-123")
         mock_collect.assert_called_once_with(mock_client, include=None, exclude=None)
-        mock_render.assert_called_once_with(mock_collect.return_value)
+        mock_render.assert_called_once_with(mock_collect.return_value, sort_key="name")
 
     @patch("gitea_dashboard.cli.render_dashboard")
     @patch("gitea_dashboard.cli.collect_all")
@@ -193,3 +193,88 @@ class TestMainWithFilters:
             main([])
 
         mock_collect.assert_called_once_with(mock_client, include=None, exclude=None)
+
+
+class TestParseArgsSort:
+    """Test --sort argument parsing."""
+
+    def test_sort_default(self):
+        """Without --sort, default is 'name'."""
+        from gitea_dashboard.cli import parse_args
+
+        args = parse_args([])
+        assert args.sort == "name"
+
+    def test_sort_issues(self):
+        """--sort issues is accepted."""
+        from gitea_dashboard.cli import parse_args
+
+        args = parse_args(["--sort", "issues"])
+        assert args.sort == "issues"
+
+    def test_sort_short_flag(self):
+        """-s activity is accepted."""
+        from gitea_dashboard.cli import parse_args
+
+        args = parse_args(["-s", "activity"])
+        assert args.sort == "activity"
+
+    def test_sort_invalid(self):
+        """--sort invalid raises SystemExit (argparse error)."""
+        from gitea_dashboard.cli import parse_args
+
+        with pytest.raises(SystemExit):
+            parse_args(["--sort", "invalid"])
+
+
+class TestParseArgsFormat:
+    """Test --format argument parsing."""
+
+    def test_format_default(self):
+        """Without --format, default is 'table'."""
+        from gitea_dashboard.cli import parse_args
+
+        args = parse_args([])
+        assert args.format == "table"
+
+    def test_format_json(self):
+        """--format json is accepted."""
+        from gitea_dashboard.cli import parse_args
+
+        args = parse_args(["--format", "json"])
+        assert args.format == "json"
+
+    def test_format_short_flag(self):
+        """-f json is accepted."""
+        from gitea_dashboard.cli import parse_args
+
+        args = parse_args(["-f", "json"])
+        assert args.format == "json"
+
+    def test_format_invalid(self):
+        """--format invalid raises SystemExit."""
+        from gitea_dashboard.cli import parse_args
+
+        with pytest.raises(SystemExit):
+            parse_args(["--format", "invalid"])
+
+
+class TestMainFormatJson:
+    """Test main() with --format json."""
+
+    @patch("gitea_dashboard.cli.collect_all")
+    @patch("gitea_dashboard.cli.GiteaClient")
+    def test_json_output(self, mock_client_cls, mock_collect, capsys):
+        """--format json produces valid JSON on stdout."""
+        import json
+
+        env = {"GITEA_TOKEN": "test-token"}
+        mock_client_cls.return_value = MagicMock()
+        mock_collect.return_value = []
+
+        with patch.dict("os.environ", env, clear=True):
+            main(["--format", "json"])
+
+        captured = capsys.readouterr()
+        parsed = json.loads(captured.out)
+        assert isinstance(parsed, list)