v0.5.3

Added

• add/start --qemu-arg <argv-element> passthrough. Repeatable, one QEMU
  argv element per occurrence (space form only), appended verbatim after
  quickchr's own args — a lab escape hatch for QEMU surface quickchr does not
  model, e.g. -M pc,pcspk-audiodev=cap -audiodev wav,id=cap,path=... to
  capture the CHR PC speaker on x86. add records the args to machine.json
  for every boot; start takes session args that replace the stored ones for
  that boot only. Library: StartOptions.qemuArgs. (#213)
• start --frozen + quickchr continue for pre-init lab workflows.
  --frozen boots held at reset (-S) with a gdbstub on
  <machineDir>/gdb.sock, skipping the boot wait; continue resumes with one
  monitor cont and waits for REST-ready by default (--no-wait to return
  immediately, --timeout-extra to extend the wait). Frozen is per-boot
  intent, not config — stop clears it and list marks frozen machines.
  set can replace or clear recorded --qemu-arg passthrough on a stopped
  machine. Library: StartOptions.frozen, instance.continue(). (#214)