Windows installer asset fix
The PyInstaller spec in windows.yml only bundled src/trcc/assets (icons / fonts / .desktop / polkit policy) — the ~600 GUI PNGs at src/trcc/ui/gui/assets/ (sidebar, tabs, theme panels, preview frames, control buttons) were never copied into the Windows .exe. _copy_assets_to_user_dir silently no-op'd because the bundled package directory didn't exist, Assets.get() returned None for every key, and the GUI rendered with empty stylesheets — a dark window with no graphics.
The macOS workflow already had the second --add-data line for the GUI assets tree. Windows just never got it. Added it to both the CLI and GUI pyinstaller invocations; mirrors macOS exactly, no app code changes.
Linux is unaffected — distribution packages (RPM / DEB / Arch) install the assets directly from the wheel layout.