Trace replay: load a trace file and step through it as a recorded history

[nkane]

Goal

A trace file from -trace is a complete instruction-by-instruction record. Loading one back into the TUI as a step-able history would let users:

• Diff a known-good trace against a divergent run, jumping to the first mismatch.
• Step forward / backward through a captured bug without re-running the CPU.
• Share traces (with consent) for debugging help.

Sketch

• New mode: chippy -replay trace.log boots without a CPU, drives the disasm + register panels from parsed trace lines.
• Stepping advances/rewinds the trace cursor; the model fakes register state from each line.
• Breakpoints become "break on PC = X" search-forward.
• Memory panel is best-effort (trace doesn't record writes — could extend the trace format with a memory-delta line later).

Acceptance

chippy -replay t.log opens a TUI that scrubs through the recorded instructions with the same UX as live debugging.

[nkane]

Rolled into the v1.0 epic at #121 — this is part of the v1.0 acceptance bar.

[nkane]

Post-1.0. Trace replay (load a trace file + step through history) is an additive feature outside the v1.0 stability bar. Deferring to v1.1.