Expose Widescreen mode choices

[mstan]

Summary:

• Renames Adaptive Widescreen to Widescreen in the launcher.
• Adds a dropdown with Dynamic as default plus fixed 4:3, 5:3, 2:1, and 21:9 modes.
• Uses only widths that the default OpenGL compute renderer supports.
• Preserves legacy adaptive-widescreen IDs; old invalid saved fixed-ratio values fall back to Dynamic.

Depends on mstan/ndsrecomp PR for --widescreen-width support.

Validation:

• mph-mod-provider-test.exe passed after rebuild.
• mph-recomp-ui.exe built successfully after rebuild.

Bead: beads-lqa.31

[mstan]

Already landed: this merged to main as b9a7339 and was then refined by 260cdcc (Constrain Widescreen mode choices), which deliberately narrowed the mode list. Shipped since v0.5.0; superseded by the constrained version.