fix: correct __main__.py entry point to import cli instead of nonexistent main

The __main__.py module was importing main from deadcode.cli but
the CLI group function is named cli. This caused python -m deadcode
to fail with ImportError.

- Fix import in __main__.py to reference cli instead of main
- Add regression test verifying python -m deadcode --help works
- Fix import ordering (ruff I001) in test_scanner.py

Author: DevForge Engineer

src/deadcode/__main__.py

@@ -1,5 +1,5 @@
 """Allow running deadcode as: python -m deadcode"""
-from deadcode.cli import main
+from deadcode.cli import cli
 
 if __name__ == "__main__":
-    main()
+    cli()

tests/test_scanner.py

@@ -6,6 +6,7 @@
 import pytest
 from deadcode.cli import cli
 from deadcode.scanner import DeadCodeScanner
+from pathlib import Path
 
 
 @pytest.fixture
@@ -292,3 +293,18 @@ def test_stats_command(self, runner, sample_project):
         assert result.exit_code == 0
         assert "Files scanned" in result.output
         assert "Unused exports" in result.output
+
+    def test_main_module_entry_point(self, runner):
+        """Test that python -m deadcode works (__main__ entry point fix)."""
+        import subprocess
+        import sys
+        result = subprocess.run(
+            [sys.executable, "-m", "deadcode", "--help"],
+            capture_output=True, text=True,
+            cwd=str(Path(__file__).parent.parent / "src"),
+        )
+        assert result.returncode == 0
+        assert "DeadCode" in result.stdout
+        assert "scan" in result.stdout
+        assert "remove" in result.stdout
+        assert "stats" in result.stdout