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/pages/Discover/DiscoverPage.tsx

@@ -376,9 +376,7 @@ function DiscoverPage() {
 			parent={parentContent}
 			current={currentContent}
 			preview={previewContent}
-			parentLabel={() => (depth() >= 1 ? "Categories" : "Up")}
 			currentLabel={currentLabel}
-			previewLabel="Detail"
 			focused={isActive}
 		/>
 	);

src/pages/Feed/FeedPage.tsx

@@ -301,9 +301,7 @@ function FeedPage() {
 			parent={parentContent}
 			current={currentContent}
 			preview={previewContent}
-			parentLabel="Up"
 			currentLabel={currentLabel}
-			previewLabel="Detail"
 			focused={isActive}
 		/>
 	);

src/pages/MyShows/MyShowsPage.tsx

@@ -432,9 +432,7 @@ export function MyShowsPage() {
 			parent={parentContent}
 			current={currentContent}
 			preview={previewContent}
-			parentLabel={() => (depth() >= 1 ? "Shows" : "Up")}
 			currentLabel={currentLabel}
-			previewLabel="Detail"
 			focused={isActive}
 		/>
 	);

src/pages/Player/PlayerPage.tsx

@@ -119,7 +119,6 @@ export function PlayerPage() {
 		<PaneRow
 			parent={parentContent}
 			current={currentContent}
-			parentLabel="Up"
 			currentLabel="Player"
 			panes={2}
 			focused={isActive}

src/pages/Search/SearchPage.tsx

@@ -431,9 +431,7 @@ function SearchPage() {
 			parent={parentContent}
 			current={currentContent}
 			preview={previewContent}
-			parentLabel={() => (depth() >= 1 ? "Query" : "Up")}
 			currentLabel={currentLabel}
-			previewLabel="Detail"
 			focused={isActive}
 		/>
 	);

src/pages/Settings/SettingsPage.tsx

@@ -267,12 +267,6 @@ export function SettingsPage() {
 		if (d === 1) return sectionForDepth1()?.label ?? "Items";
 		return editorItem()?.label ?? "Editor";
 	};
-	const parentLabel = () => {
-		const d = depth();
-		if (d === 1) return "Sections";
-		if (d === 2) return sectionForDepth1()?.label ?? "";
-		return "Up";
-	};
 
 	// ── parent pane: previous-depth list (blank at depth 0) ────────────────
 	// Sibling <Show> blocks per depth (mirrors the preview pane) so Solid
@@ -384,9 +378,7 @@ export function SettingsPage() {
 			parent={parentContent}
 			current={currentContent}
 			preview={previewContent}
-			parentLabel={parentLabel}
 			currentLabel={currentLabel}
-			previewLabel="Detail"
 			focused={isActive}
 		/>
 	);