Capture real-hardware performance matrix

[tsotchke]

Add measured physical-machine performance rows for the preview release model set.

Start with one 486-class default-model run, then add optional comparison rows for speed and low-memory release modes.

Acceptance criteria:

• physical capture staged with scripts/stage_hardware_capture_evidence.py
• scripts/hardware_performance_matrix.py includes at least one physical-machine row
• README and release notes keep QEMU-vs-physical claims separated

Pentium data is useful as scaling evidence but does not replace the 486-class baseline.