fix(gallery): force light color-scheme in MCP iframe + A2UI host

The MCP Apps bundle declared color-scheme: light dark but the CSS variables
only had light-mode values, leaving dark-mode OS users with dark text on a
dark UA canvas. The @a2ui/lit renderer respected prefers-color-scheme too,
muting "Latest" and subtitles into the gallery's light card background.

Force light mode in both surfaces and give the MCP body an opaque white
background so the iframe canvas can't bleed through.

Author: mirkokiefer

gallery/build.ts

@@ -286,6 +286,10 @@ main { max-width: 1400px; margin: 0 auto; padding: 32px 24px 80px; }
   border: 1px solid var(--border);
   border-radius: 8px;
   padding: 12px;
+  /* Gallery is light-themed; force the lit renderer's CSS to render
+   * in light mode regardless of OS preference. color-scheme inherits
+   * into the component's shadow DOM. */
+  color-scheme: light;
 }
 .a2ui-host[data-mounted="0"]::after {
   content: "loading @a2ui/lit from esm.sh…";
@@ -370,6 +374,7 @@ main { max-width: 1400px; margin: 0 auto; padding: 32px 24px 80px; }
   border: 0;
   border-radius: 8px;
   background: white;
+  color-scheme: light;
 }
 .mcp-attribution {
   font-size: 11px; color: var(--muted); margin-top: 8px;