every theme declares the mark

The logo is now stated by each of the fourteen themes rather than supplied by a default
none of them mentions. The base default stays empty, which is the right answer for a
theme written by a stranger — showing nothing beats showing someone else's brand.

Explicit costs one line and buys two things: a theme that ships a brand says so, and a
white-labelled build replaces a line it can see instead of hunting for the default that
was quietly doing the work.

Verified in the browser across four themes.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/workspaces/theme/css/themes/gruvbox.css

@@ -9,6 +9,11 @@
 */
 
 [data-theme='gruvbox'] {
+  /* The mark. Declared by every theme rather than inherited from a default: a theme that ships a
+     brand should say so, and a white-labelled build replaces this line rather than hunting for the
+     default that was quietly supplying it. */
+  --logo-src: '/officer-logo.svg';
+
   --radius: 0.625rem;
   --background: #282828;
   --foreground: #ebdbb2;