[djcesar]

Summary

Adds a small chain-link ToolButton (🔗) next to the existing switch-width/height button (⇅) in three places:

• txt2img — Width/Height
• img2img — "Resize to" tab
• Extras — "Scale to" tab

When toggled on, it captures the current width/height ratio, and from then on editing either field — by typing in the number box or by dragging the slider — automatically recalculates the other field to keep that ratio, rounded to the field's step and clamped to its min/max. Toggling it off lets both fields move independently again, as today.

This is a small quality-of-life addition for anyone resizing/upscaling to a specific target resolution who wants to keep the source aspect ratio without doing the math by hand or re-checking it after every edit.

Screenshots

Off (default):
Width and Height sliders behave exactly as before.

On:
The link button gets a solid highlighted background (reusing the theme's --primary-600, the same color used elsewhere for primary actions) so its state is clear at a glance. Dragging Width from 432 to 1024 (with Height starting at 768) automatically moves Height to 1816, preserving the original ~0.748 ratio.

Implementation notes

• javascript/ui.js: toggleResLinkFor(linkBtnId, widthElemId, heightElemId) and setupResLinkFor(linkBtnId, widthElemId, heightElemId, minVal, maxVal, step) hold the actual linking logic. They listen on both input[type=number] and input[type=range] for each field, since Gradio's Slider renders both and either one can be the source of a user edit. toggleResLink(tabname) / setupResLink(tabname) are thin convenience wrappers for the common "{tabname}_width" / "{tabname}_height" elem_id convention already used by txt2img/img2img, so existing call sites stay simple.
• A recursion guard (state.syncing) prevents the programmatic update of the "other" field from re-triggering the handler.
• Extras' "Scale to" fields go up to 8192 (vs. 2048 for txt2img/img2img), so it calls setupResLinkFor(...) directly with its own range rather than using the tabname-convention wrapper.
• modules/ui.py / scripts/postprocessing_upscale.py: new ToolButton per location, wired with fn=None, _js="...", following the exact same pattern already used by the neighboring switch-width/height button.
• style.css: .res-link-enabled gives the button an opaque background while active instead of a subtle transparency overlay, for better at-a-glance visibility.

Test plan

• Toggled the link on in txt2img, dragged the Width slider, confirmed Height updates to keep the ratio, and vice versa.
• Same test in img2img "Resize to" and in Extras "Scale to" (confirmed the 8192 max is respected there, not clamped to 2048).
• Confirmed typing directly in the number field also triggers the sync (not just dragging).
• Toggled the link off and confirmed both fields go back to moving independently.
• Checked the browser console for errors during all of the above — none.