[#109.2] Fix asymmetric resize behavior - components should maintain FIXED size in both directions

[thomasnemer]

Parent Issue

Part of #109 - Window resize behavior conflicts with component sizing

Problem

Components with AxisResizeBehavior::FIXED appear to grow when the window expands, but do not shrink back when the window contracts.

Expected: Components with FIXED axis behavior should maintain their original size regardless of window resize direction.

Observed: Fixed-size components still affected by layout during shrinking operations.

Potential Causes

• Interaction between FlexLayout's shrink factors and component resize behavior
• Min/max size constraints not being properly applied
• Original dimensions being recalculated incorrectly during shrink operations
• setBounds() calls from layout manager overriding resize behavior

Reproduction

1. Build and run the demo app: mise demo
2. Expand window vertically - observe panel heights
3. Shrink window vertically - observe if panels shrink correctly (they shouldn't if FIXED)
4. Repeat with horizontal resizing

Success Criteria

• FIXED components maintain original size during window expansion
• FIXED components maintain original size during window contraction
• Behavior is symmetric in both resize directions
• Test in demo app with left panel (300px width) and right panel (320px width)
• Add/update unit tests for symmetric resize behavior

Related Code

• include/bombfork/prong/core/component.h - onParentResize(), setBounds()
• include/bombfork/prong/layout/flex_layout.h - shrink factor interaction
• tests/test_axis_resize.cpp

Dependencies

Should be worked on after #109.1 to ensure baseline behavior is correct.