fix: require edit mode for separator changes

[cmdr-chara]

Summary

Prevents separator controls from changing the bar layout while the bar is locked.

• Require barUnlocked for V1 within-region split handles.
• Require barUnlocked for V1 left/center/right boundary split handles.
• Require barUnlocked for V2 separator handles.
• Add a regression script that checks all three edit handles remain gated by unlock mode.

Why

Separator MouseAreas were still active when the layout was locked, so an ordinary click near a separator could accidentally merge or split bar sections. This could, for example, join the center and right sections into one large pill.

The change keeps separator editing available in edit mode while making the locked layout read-only.

Scope

This is intentionally small: it does not change separator persistence, drag-and-drop behavior, bar geometry, or styling.

Regression coverage

tests/qs-bar-edit-lock-regression.sh verifies that the V1 mkMa and bMa handles and the V2 sepMa handle all require barSlot.root.barUnlocked.