feat(tools): pywebview bootstrap + python bridge API

Single window (900x720, dark background) loading web/index.html with a
Python bridge exposing list_existing_commands, list_exes,
list_sound_names, preview_sound, slugify, validate_draft, save_command,
plus llm_suggest hook for M3. Sound preview spawned on a daemon thread
so the GUI does not block.

tools/command_builder/__main__.py

@@ -0,0 +1,4 @@
+from tools.command_builder.app import main
+
+if __name__ == "__main__":
+    main()