fix(embeds): GIF previews keep their own size and shape (#341)

Giphy and Tenor link previews forced every GIF into the same box — full
card width, max 200px tall, object-fit: cover — whatever its shape: a
square GIF lost half its height, a portrait one three quarters (only the
middle band showed, so captions and faces at the top/bottom were cut), and
a 100×80 GIF was blown up 4×.

utils/gifPreviewSize.ts (unit-tested) fits the GIF inside 400×320 from
og:image:width/height, keeping its aspect ratio and enlarging small GIFs
at most 2×. The card centres the GIF on the surface colour with
object-fit: contain, reserves the box before it loads, and the GIF badge
sits on the GIF's corner. Without dimensions it shows at natural size,
capped by the card. The >10 MB thumbnail fallback is requested at 2× the
box (800×640) so it isn't upscaled.

Verified headless (fixture previews, desktop / Pixel 7 / 320px phone):
480×200 → 398×166, 300×300 → 320×320 (292×292 on 320px), 240×480 →
160×320, 100×80 → 200×160, all 100% visible; the no-dimension fallback
and narrow cards keep the ratio. tsc clean, 1325 unit tests pass, eslint
0 errors (36 warnings, unchanged), prettier clean.

Fixes #341

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src/app/components/url-preview/UrlPreviewCard.tsx

@@ -13,6 +13,7 @@ import {
   as,
   color,
   config,
+  toRem,
 } from 'folds';
 import { ImageOverlay } from '../ImageOverlay';
 import { MobileTouchTarget } from '../../styles/mobile.css';
@@ -48,6 +49,11 @@ import {
   tiktokOembedUrl,
   tiktokPlayerEmbedUrl,
 } from '../../utils/videoEmbed';
+import {
+  GIF_PREVIEW_MAX_HEIGHT,
+  GIF_PREVIEW_MAX_WIDTH,
+  gifPreviewBox,
+} from '../../utils/gifPreviewSize';
 
 const linkStyles = { color: color.Success.Main };
 
@@ -2277,6 +2283,9 @@ function GifCard({
 }) {
   const title = (prev['og:title'] as string | undefined) ?? '';
   const mxcImage = prev['og:image'] as string | undefined;
+  // Size the GIF from its own dimensions (Giphy and Tenor publish them) rather
+  // than forcing every GIF into one cropped band.
+  const box = gifPreviewBox(prev['og:image:width'], prev['og:image:height']);
 
   // A GIF card exists to show a moving GIF, so request the original rather than
   // a thumbnail — the thumbnail endpoint would return a frozen first frame.
@@ -2284,7 +2293,15 @@ function GifCard({
   const thumbSrc = mxcImage
     ? shouldServeGifOriginal(url, prev)
       ? mxcUrlToHttp(mx, mxcImage, useAuthentication)
-      : mxcUrlToHttp(mx, mxcImage, useAuthentication, 400, 200, 'scale', false)
+      : mxcUrlToHttp(
+          mx,
+          mxcImage,
+          useAuthentication,
+          GIF_PREVIEW_MAX_WIDTH * 2,
+          GIF_PREVIEW_MAX_HEIGHT * 2,
+          'scale',
+          false,
+        )
     : null;
 
   // If there's no image, fall back to a generic-style layout
@@ -2316,7 +2333,9 @@ function GifCard({
 
   return (
     <Box direction="Column" style={{ width: '100%' }}>
-      {/* GIF thumbnail — full width */}
+      {/* The whole GIF at its own aspect ratio, centred; never cropped. With a
+          known size the box is reserved before it loads (no layout jump);
+          without one it shows at its natural size, capped by the card. */}
       <a
         href={url}
         target="_blank"
@@ -2324,8 +2343,22 @@ function GifCard({
         className={previewCss.GifThumbnailWrapper}
         aria-label={`View GIF on ${siteBadgeLabel}: ${title}`}
       >
-        <img className={previewCss.GifThumbnailImg} src={thumbSrc} alt={title} loading="lazy" />
-        <span className={previewCss.GifBadge}>GIF</span>
+        <span className={previewCss.GifFrame}>
+          <img
+            className={previewCss.GifThumbnailImg}
+            src={thumbSrc}
+            alt={title}
+            loading="lazy"
+            width={box?.width}
+            height={box?.height}
+            style={
+              box
+                ? { width: toRem(box.width), aspectRatio: `${box.width} / ${box.height}` }
+                : undefined
+            }
+          />
+          <span className={previewCss.GifBadge}>GIF</span>
+        </span>
       </a>
       {/* Footer row */}
       <UrlPreviewContent>