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/pages/Workspace.tsx

@@ -621,7 +621,7 @@ export function Workspace() {
         <div className={`flex min-h-0 flex-1 gap-4${home ? " hidden" : ""}`}>
           <section
             data-testid="lane-detail"
-            className={`flex min-h-0 min-w-0 flex-1 flex-col ${currentLane ? "card p-4" : ""}${
+            className={`flex min-h-0 min-w-0 flex-1 flex-col${
               currentLane && changesOpen && changesSize === "full" ? " hidden" : ""
             }`}
           >
@@ -795,7 +795,9 @@ export function Workspace() {
               <aside
                 id="lane-changes-panel"
                 data-testid="lane-changes-card"
-                className={`card flex shrink-0 flex-col p-3 ${CHANGES_WIDTH[changesSize]}`}
+                className={`flex shrink-0 flex-col ${CHANGES_WIDTH[changesSize]}${
+                  changesSize === "full" ? "" : " border-l border-border pl-4"
+                }`}
               >
                 {/* Activity bar: Files · Changes · Sessions, then the resize control. */}
                 <div className="mb-2 flex items-center gap-1" role="toolbar">
@@ -891,7 +893,7 @@ export function Workspace() {
                 aria-controls="lane-changes-panel"
                 aria-label={tLanes("changes.expand")}
                 title={tLanes("changes.expand")}
-                className="card flex w-9 shrink-0 flex-col items-center gap-2 py-3 text-fg-muted transition-colors hover:text-fg-primary"
+                className="flex w-9 shrink-0 flex-col items-center gap-2 border-l border-border py-3 text-fg-muted transition-colors hover:text-fg-primary"
               >
                 <PanelLeftClose className="h-4 w-4" />
                 <span className="text-[10px] uppercase tracking-wide [writing-mode:vertical-rl]">