feat(workspace): session view and right panel sit on the page, no cards

The session section and the Files/Changes panel drop their cards; one
vertical divider separates them (none at full width), and the collapsed
rail keeps only that divider. The terminal goes back to the page colour
(--surface-0), and the panel's two sticky bars cover scrolled content in
the page colour instead of the card's.

Inside, the git row loses its bordered box for a bottom divider, and the
ended-session prompt box drops its own fill and shadow.

client/src/lib/terminalTheme.ts

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