Fix resume-at-line WCS recovery after G53

[righteousgambit]

Closes #665

Summary

Exclude non-modal G53 from resume-at-line's active-WCS search while preserving the controller's explicit G53 G0 Z-2 recovery move.

Changes

• Remove G53 from the modal WCS candidates used by playStartLineCommand().
• Add a regression test with G55 followed by a G53 machine-coordinate move.
• Add an unreleased changelog entry.

Why

G53 applies machine coordinates to its associated movement; it does not select a persistent coordinate system. Treating it as the most recent WCS can prevent resume-at-line from restoring the program's actual G54-G59.3 state.

This is state-dependent: if the machine already retains the intended WCS, behavior may be unchanged. The fix removes that dependency and makes resume reconstruction deterministic.

Validation

• Regression against the pinned develop implementation: 1 failed because the preview contained bare buffer G53 and omitted the expected buffer G55.
• With this change, using the same exact-ref sparse harness: PYTHONDONTWRITEBYTECODE=1 PYTHONPATH=/tmp/carvera-test-stubs:. pytest -q tests/unit/test_resume_wcs.py -> 1 passed.
• ruff check carveracontroller/Controller.py tests/unit -> passed.
• git diff --check develop...HEAD -> passed.

Real branch verification

The repository's locked Poetry environment was installed from poetry.lock. The targeted suite passed on real fork commit d989beb58eaa, whose sole parent is pinned upstream develop@2ea66c10e96d88013a04441134d3d4f8e8c88510.

poetry run pytest -q tests/unit/test_resume_wcs.py

Result: 1 passed.

Quality gates on the real branch:

• Ruff check: passed
• Ruff format --check: passed
• git diff --check 2ea66c10e96d88013a04441134d3d4f8e8c88510..d989beb58eaafc7792eead19cff4a89fabb8f3a6: passed