FR: Create capture areas with fixed aspect ratios

[boosh]

It'd be great if the area selection mode allowed constraining the recording area to a specific aspect ratio (and even better if it shipped with common presents for e.g. youtube/social media apps).

[linear]

CAP-687

[tembo]

The capture area selection already has solid aspect ratio infrastructure that would support this feature. The Cropper component (apps/desktop/src/components/Cropper.tsx) already handles constrained aspect ratios - it supports passing an aspectRatio prop and has logic for snapping to common ratios like 1:1, 16:9, 9:16, etc. (see COMMON_RATIOS on line 80).

The capture area UI (apps/desktop/src/routes/capture-area.tsx) already has an aspect ratio button that opens a menu via showCropOptionsMenu - selecting a ratio from this menu locks the selection to that aspect. The menu includes all the common ratios plus a "Free" option and "Snap to ratios" toggle (see createCropOptionsMenuItems at line 1493 of the Cropper component).

For the preset request specifically (YouTube, social media), the editor already defines social-friendly presets in apps/desktop/src/routes/editor/projectConfig.ts:

export const ASPECT_RATIOS = {
  wide: { name: "Wide", ratio: [16, 9] },      // YouTube landscape
  vertical: { name: "Vertical", ratio: [9, 16] }, // TikTok/Reels/Shorts  
  square: { name: "Square", ratio: [1, 1] },   // Instagram feed
  classic: { name: "Classic", ratio: [4, 3] },
  tall: { name: "Tall", ratio: [3, 4] },
};

The feature could be implemented by either extending COMMON_RATIOS with named presets and updating the menu items to show friendly names (e.g. "YouTube 16:9", "TikTok 9:16"), or by adding a separate "Presets" submenu to the capture area's aspect ratio dropdown.

Related: #1581 covered custom aspect ratios in the editor export (already implemented), and #1079 introduced the current unified Cropper component.