feat: --commit flag (#44)

- --commit: после генерации отчёта сохраняет период в
  period.last_used.from/to YAML-конфига
- При period.dynamic=true следующий запуск вычисляет период от last_used:
  полный месяц → следующий месяц, произвольный диапазон → та же длина
- При period.dynamic=false перезаписывает default_from/default_to
- При period.precision=datetime сохраняет timestamps с точностью до секунд
- --commit без --output сохраняет отчёт по шаблону из конфига
- compute_next_period() в config.py
- save_period_to_config() в yaml_config.py
- 23 новых теста (7 CLI, 6 config, 6 yaml, 4 date_range)

Closes #44

tests/test_yaml_config.py

@@ -206,3 +206,115 @@ class TestResolveOutputPath:
 
         result = resolve_output_path("unknown_format")
         assert result == "unknown_format.xlsx"
+
+
+class TestSavePeriodToConfig:
+    """Tests for save_period_to_config()."""
+
+    def test_creates_last_used_in_empty_config(self, tmp_path):
+        import yaml
+
+        from redmine_reporter.yaml_config import save_period_to_config
+
+        config_path = tmp_path / "config.yml"
+        save_period_to_config(str(config_path), "2026-06-01", "2026-06-30", "date", True)
+
+        with open(config_path) as fh:
+            data = yaml.safe_load(fh)
+
+        assert data["period"]["last_used"]["from"] == "2026-06-01"
+        assert data["period"]["last_used"]["to"] == "2026-06-30"
+        assert "default_from" not in data["period"]
+
+    def test_overwrites_existing_last_used(self, tmp_path):
+        import yaml
+
+        from redmine_reporter.yaml_config import save_period_to_config
+
+        config_path = tmp_path / "config.yml"
+        config_path.write_text(
+            "period:\n" "  last_used:\n" "    from: '2026-05-01'\n" "    to: '2026-05-31'\n"
+        )
+
+        save_period_to_config(str(config_path), "2026-06-01", "2026-06-30", "date", True)
+
+        with open(config_path) as fh:
+            data = yaml.safe_load(fh)
+
+        assert data["period"]["last_used"]["from"] == "2026-06-01"
+        assert data["period"]["last_used"]["to"] == "2026-06-30"
+
+    def test_dynamic_false_overwrites_defaults(self, tmp_path):
+        import yaml
+
+        from redmine_reporter.yaml_config import save_period_to_config
+
+        config_path = tmp_path / "config.yml"
+        config_path.write_text(
+            "period:\n" "  default_from: '2026-01-01'\n" "  default_to: '2026-01-31'\n"
+        )
+
+        save_period_to_config(str(config_path), "2026-06-01", "2026-06-30", "date", False)
+
+        with open(config_path) as fh:
+            data = yaml.safe_load(fh)
+
+        assert data["period"]["default_from"] == "2026-06-01"
+        assert data["period"]["default_to"] == "2026-06-30"
+        assert data["period"]["last_used"]["from"] == "2026-06-01"
+        assert data["period"]["last_used"]["to"] == "2026-06-30"
+
+    def test_datetime_precision_stores_timestamps(self, tmp_path):
+        import yaml
+
+        from redmine_reporter.yaml_config import save_period_to_config
+
+        config_path = tmp_path / "config.yml"
+
+        save_period_to_config(
+            str(config_path),
+            "2026-06-30T09:00:00",
+            "2026-06-30T12:00:00",
+            "datetime",
+            True,
+        )
+
+        with open(config_path) as fh:
+            data = yaml.safe_load(fh)
+
+        assert data["period"]["last_used"]["from"] == "2026-06-30T09:00:00"
+        assert data["period"]["last_used"]["to"] == "2026-06-30T12:00:00"
+
+    def test_preserves_existing_sections(self, tmp_path):
+        import yaml
+
+        from redmine_reporter.yaml_config import save_period_to_config
+
+        config_path = tmp_path / "config.yml"
+        config_path.write_text(
+            "redmine:\n"
+            "  url: https://example.com\n"
+            "  author: Test\n"
+            "output:\n"
+            "  dir: /tmp\n"
+        )
+
+        save_period_to_config(str(config_path), "2026-06-01", "2026-06-30", "date", True)
+
+        with open(config_path) as fh:
+            data = yaml.safe_load(fh)
+
+        assert data["redmine"]["url"] == "https://example.com"
+        assert data["redmine"]["author"] == "Test"
+        assert data["output"]["dir"] == "/tmp"
+        assert data["period"]["last_used"]["from"] == "2026-06-01"
+
+    def test_sets_permissions_0600(self, tmp_path):
+        from redmine_reporter.yaml_config import save_period_to_config
+
+        config_path = tmp_path / "config.yml"
+
+        save_period_to_config(str(config_path), "2026-06-01", "2026-06-30", "date", True)
+
+        mode = config_path.stat().st_mode & 0o777
+        assert mode == 0o600