options: enforce minimum window size to prevent controls disappearing on resize

[Zack-src]

• The options dialog had no minimum size constraint - resizing too small caused all controls to collapse/disappear off-screen.
• Added WM_SIZING handler with PhResizingMinimumSize preventing the window from going below its initial dialog size (423×247 DU, converted to pixels via MapDialogRect at dialog creation).

Test

1. Open Options
2. Try to drag any edge/corner to make the window very small
3. Window should stop shrinking at its default size