feat(workspace): frameless console that blends into its card

The tab bar and terminal lose their bordered box: the bar keeps one
divider with an accent underline on the active tab, and the terminal is
painted in the card's colour (--surface-3) instead of the page's.

That made a long-standing overflow visible: xterm re-measures its cell
only on a font option change or a resize, so a webfont landing after
open left the fit on the fallback font's cell and the rows/cols spilled
out of the pane. Re-set the family and refit on document.fonts
loadingdone.

client/src/lib/terminalTheme.ts

@@ -54,10 +54,11 @@ export function buildTerminalTheme(read: VarReader): ITheme {
   const magenta = "#c678dd";
   const cyan = "#56b6c2";
   return {
-    background: v("--surface-0"),
+    // The `.card` colour: the console sits on a card, with no frame between.
+    background: v("--surface-3"),
     foreground: v("--fg-primary"),
     cursor: v("--fg-primary"),
-    cursorAccent: v("--surface-0"),
+    cursorAccent: v("--surface-3"),
     selectionBackground: v("--border-light"),
     black: v("--border-light"),
     red,