Restore center-pane borders, move title to top-left slot

- Current pane gets muted left/right borders only (no full box, no accent
  ring); border colors are passed only when a border is requested, since
  opentui flips borderless boxes to bordered when borderColor is supplied.
- Remove the Up / <current tab> / Detail titles above the panes; the current
  pane's title now renders once, top-left in the parent column's header slot.
- Drop the parentLabel/previewLabel props from PaneRow and all callers.
- Remove the tab/depth indicator from the bottom-left of the status bar.
- Tests measure column widths from the border glyphs and assert the
  left/right edges render muted regardless of focus.

src/components/Shell.tsx

@@ -23,20 +23,11 @@ import { useAppStore } from "@/stores/app";
 import { useToast } from "@/ui/toast";
 import { emit, on } from "@/utils/event-bus";
 import { LayerGraph } from "@/utils/layer-graph";
-import { TABS, TabPaneCount } from "@/utils/navigation";
+import { TABS } from "@/utils/navigation";
 import { createDispatcher } from "@/utils/dispatch";
 import { TabListPane } from "@/components/TabPanel";
 import { PaneRow } from "@/components/PaneRow";
 
-const TAB_LABEL: Record<TABS, string> = {
-	[TABS.FEED]: "Feed",
-	[TABS.MYSHOWS]: "My Shows",
-	[TABS.DISCOVER]: "Discover",
-	[TABS.SEARCH]: "Search",
-	[TABS.PLAYER]: "Player",
-	[TABS.SETTINGS]: "Settings",
-};
-
 export function Shell() {
 	const theme = useTheme();
 	const t = theme.theme;
@@ -271,9 +262,7 @@ export function Shell() {
 								<text fg={t.textMuted}>j/k move · l/Enter open a tab</text>
 							</box>
 						}
-						parentLabel="Up"
 						currentLabel="Tabs"
-						previewLabel=""
 						focused
 					/>
 				</Show>
@@ -296,15 +285,6 @@ export function Shell() {
 							<text fg={t.accent} paddingLeft={1}>
 								{modeLabel()}
 							</text>
-							<text fg={t.textMuted} paddingLeft={1}>
-								{nav.atRootTab()
-									? "Tabs · root"
-									: `${TAB_LABEL[nav.activeTab()]} · ${
-											nav.isDepthTab()
-												? `depth ${nav.currentDepth()}`
-												: `pane ${nav.activePane()}/${TabPaneCount[nav.activeTab()]}`
-										}`}
-							</text>
 							<Show when={nav.selectedIds().length > 0}>
 								<text fg={t.warning} paddingLeft={1}>
 									● {nav.selectedIds().length}