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/pages/Workspace.tsx

@@ -180,11 +180,7 @@ function ConsoleArea({
           actions={<LaneToolsMenu lane={lane} />}
         />
       )}
-      <div
-        className={`flex min-h-0 flex-1 flex-col border border-border bg-surface-0 p-2 ${
-          lane ? "rounded-b-lg" : "rounded-lg"
-        }`}
-      >
+      <div className="flex min-h-0 flex-1 flex-col pt-2">
         {slots.map((slot) => (
           <div key={slot} className={slot === activeSlot ? "contents" : "hidden"}>
             <LaneConsolePane

client/src/pages/__tests__/__snapshots__/screens.snapshot.test.tsx.snap

@@ -5413,7 +5413,7 @@ exports[`screen snapshots > Run 1`] = `
                 class="flex min-h-0 flex-1 flex-col"
               >
                 <div
-                  class="flex min-h-0 flex-1 flex-col border border-border bg-surface-0 p-2 rounded-lg"
+                  class="flex min-h-0 flex-1 flex-col pt-2"
                 >
                   <div
                     class="contents"