Check AROS compatibility

[sidick]

AmiPilot currently targets classic AmigaOS (2.04/V37 floor, OS 3.1/68020
recommended — see CLAUDE.md's "Minimum requirements"). Worth a pass at
some point to check how much of the stack (intuition-model's walker,
amiinspect, AmiPilotServer, the manifest format) works unmodified
against AROS, and what would need adapting:

• LockIBase()/structural-walk discipline — same Intuition semantics on
  AROS, but worth confirming against its actual implementation rather
  than assuming.
• GadTools/BOOPSI classification (ClassifyGadget/ClassifyByClassID) —
  AROS ships its own gadtools.library/reaction; role mapping may need
  verification, especially the GTYP_BOOLGADGET button/checkbox
  discrimination workaround.
• Toolchain: currently built with Bebbo's m68k-amigaos GCC
  (-m68000 -msoft-float -noixemul, libnix). AROS has its own SDK/ABI
  (and runs natively on x86/ARM/etc, not just m68k) — a real second
  build target, not just a recompile.
• TCP/serial transport and the ARexx port — AROS's arexx/rexxsyslib
  compatibility and networking stack would need their own check.

Not blocking any current phase; filed to track as a future
compatibility pass, likely after v1.0 given the existing phase
sequencing in docs/implementation-plan.md.