Latest QMK Firmware

NAV: add media/mods/clipboard, clean up dead code

- NAV left half: media keys (vol), real GACS mods for
  sustained modifier+arrow, Ctrl+ZXCV clipboard shortcuts
- SYM: remove duplicate grave/tilde from bottom row
- Remove unused HOME_ROW_MOD_GACS, POINTER_MOD, _L_PTR macros
- Tighten NUM right-half numpad spacing
- Align NAV columns consistently

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>