feat: add emulated mouse driver, file output, and GUI mouse grab

feat: add emulated mouse driver, file output, and GUI mouse grab

- machine/: 1 MiB emulated RAM behind DEF SEG/PEEK/POKE, with the
  qbext mouse TSR always loaded (INT 79h vector, 8-byte table: magic,
  X/Y accumulators, button latch; accumulate + read-and-reset)
- mouse input: SwingFrontend pushes scaled window deltas and button
  latches; GameDriver gains scripted --mouse deltas/buttons for
  headless verification; mousedrv.bas runs unmodified
- GUI mouse grab: first click captures (transparent always-on-top
  overlay spans all screens, cursor hidden), Ctrl+F10 releases; no
  Robot warping (Wayland RemoteDesktop popup, Xvfb EDT hang)
- language: VAL parses &H/&O with signed literal semantics, HEX$,
  LOCATE with omitted column, OPEN FOR OUTPUT/APPEND + PRINT # (CRLF,
  console formatting), CHDIR/MKDIR with DOS path semantics
  (backslashes, drive letters, case-insensitive components)
- SCREEN 13 default foreground corrected to 15 (QB.EXE/DOSBox oracle;
  255 is black in the BIOS palette, so text printed black-on-black)