feat: add regenerate command to force rebuild of specific targets

The regenerate command accepts one or more target names and forces them
to be rebuilt even if they are up to date. This respects the
archive_folder setting, archiving previous versions before overwriting.

tests/test_cli.py

@@ -136,6 +136,59 @@ class TestBuildCommand:
         assert call_args[0][3] == "output.txt"
 
 
+class TestRegenerateCommand:
+    """Test the regenerate CLI command."""
+
+    def test_regenerate_forces_rebuild(self, cli_project: Path) -> None:
+        build_result = BuildResult(
+            built=["output.txt"], skipped=["image.png"], failed={}
+        )
+        with (
+            patch("hokusai.cli.Path") as mock_path_cls,
+            patch(
+                "hokusai.cli.run_build",
+                new_callable=AsyncMock,
+                return_value=build_result,
+            ) as mock_run,
+        ):
+            mock_path_cls.cwd.return_value = cli_project
+            result = runner.invoke(app, ["regenerate", "output.txt"])
+
+        assert result.exit_code == 0
+        assert "1 regenerated" in result.output
+        # Check force_dirty was passed
+        call_kwargs = mock_run.call_args[1]
+        assert call_kwargs["force_dirty"] == {"output.txt"}
+
+    def test_regenerate_multiple_targets(self, cli_project: Path) -> None:
+        build_result = BuildResult(
+            built=["output.txt", "image.png"], skipped=[], failed={}
+        )
+        with (
+            patch("hokusai.cli.Path") as mock_path_cls,
+            patch(
+                "hokusai.cli.run_build",
+                new_callable=AsyncMock,
+                return_value=build_result,
+            ) as mock_run,
+        ):
+            mock_path_cls.cwd.return_value = cli_project
+            result = runner.invoke(app, ["regenerate", "output.txt", "image.png"])
+
+        assert result.exit_code == 0
+        assert "2 regenerated" in result.output
+        call_kwargs = mock_run.call_args[1]
+        assert call_kwargs["force_dirty"] == {"output.txt", "image.png"}
+
+    def test_regenerate_unknown_target(self, cli_project: Path) -> None:
+        with patch("hokusai.cli.Path") as mock_path_cls:
+            mock_path_cls.cwd.return_value = cli_project
+            result = runner.invoke(app, ["regenerate", "nonexistent.txt"])
+
+        assert result.exit_code == 1
+        assert "Unknown target(s): nonexistent.txt" in result.output
+
+
 class TestCleanCommand:
     """Test the clean CLI command."""