[codex] Limit crop zoom for mask editing

[muukii]

Summary

• Add a finite maximum crop zoom based on a minimum authored crop-output side length.
• Clamp programmatic crop zoom to the scroll view's configured zoom range before calculating content offset.
• Add focused tests for the crop zoom policy on large and small images.

Root Cause

Crop editing allowed an unbounded zoom scale, so users could author a final crop output that was only a few pixels wide or tall. Blur masking uses that final crop output as the tool canvas; once the crop output became extremely small, the tool surface entered huge zoom-scale space and viewport-sized brushes resolved into sub-pixel image-space strokes.

Validation

• BrightroomEngineTests/CropEditingZoomScaleTests via XcodeBuildMCP: 2 tests passed
• git diff --check