fix(mister): derive frontend aspect ratio from active output

[zaparoo-automation-bot]

The former Resolution picker changed frontend framebuffer geometry without changing MiSTer’s physical output timing. The attached photos show the result: 2560x1440 fills the output with incorrect logical scaling, while 1920x1080 occupies only part of the active scanout and becomes letterboxed.

Frontend PR #377 and paired ZaparooProject/Main_MiSTer#15 replace manual geometry with output-derived scaling:

• Remove the MiSTer resolution picker.
• Wait for Main to settle active HDMI timing before frontend spawn.
• Derive logical framebuffer size from active output geometry.
• Handle MiSTer pixel-repetition modes in Main’s scale-relative framebuffer commands.
• Use 1280x720 logical geometry for mode 14’s 2560x1440 physical output.
• Preserve mapped geometry through frontend respawn and game return.

Implementation and validation are tracked in frontend #377 and ZaparooProject/Main_MiSTer#15.

[wizzomafizzo]

Closing as addressed by open frontend PR #377 and paired Main_MiSTer PR #15. Remaining merge and validation status stays on those PRs.