fix(installer): make window resizable and harden layouts for large sy…

[kev1n77]

• allow installer window resizing and raise default size with minimum bounds
• add shared scrollable page shell with fixed action footer
• refactor language, options, progress, theme, and uninstall pages to avoid clipped buttons
• replace absolute-positioned uninstall actions with normal responsive footer layout
• make theme selection grid responsive to reduced width and larger text sizes
• add footer/button wrapping behavior for narrow windows and enlarged fonts