post: cap embedded video/iframe to the column (1920px clip overflowed), swap demo to the 2 s 1080p take

src/styles/global.css

@@ -189,6 +189,26 @@ a { color: var(--brand); text-decoration: none; }
 a:hover { color: var(--brand-soft); }
 article a { text-decoration: underline; text-underline-offset: 2px; }
 
+/* Raw HTML in a post body keeps its source width — a 1920px CDN <video> or a
+   full-size <img> overflows the column and forces a horizontal scrollbar. Cap
+   everything to the text column; `height:auto` preserves the intrinsic ratio
+   (never set a fixed aspect-ratio here, clips have different shapes). */
+article video,
+article iframe {
+  display: block;
+  width: 100%;
+  max-width: 100%;
+  height: auto;
+  margin: 1.75rem 0;
+  border-radius: var(--radius);
+  border: 1px solid var(--border);
+  background: #000;
+}
+article img {
+  max-width: 100%;
+  height: auto;
+}
+
 time { color: var(--faint); font-size: 0.88rem; }
 
 /* Light theme: the v2 artwork is a near-black viewport, so on a white page it reads as