TUI: optimize fuzzy filtering and consolidate time formatting

- Extract formatRelativeTime to shared utility for reuse across components
- Optimize FilterableSelectList with pre-lowercased searchTextLower field (avoids toLowerCase on every keystroke)
- Implement custom fuzzy matching with space-separated token support and word boundary scoring
- Use matchesKey utility for consistent keybinding handling (arrows, vim j/k, ctrl+p/n)
- Fix searchable-select-list to support vim keybindings consistently
- Fix system-prompt runtimeInfo null check with nullish coalescing operator

src/utils/time-format.ts

@@ -0,0 +1,15 @@
+export function formatRelativeTime(timestamp: number): string {
+	const now = Date.now();
+	const diff = now - timestamp;
+	const seconds = Math.floor(diff / 1000);
+	const minutes = Math.floor(seconds / 60);
+	const hours = Math.floor(minutes / 60);
+	const days = Math.floor(hours / 24);
+
+	if (seconds < 60) return "just now";
+	if (minutes < 60) return `${minutes}m ago`;
+	if (hours < 24) return `${hours}h ago`;
+	if (days === 1) return "Yesterday";
+	if (days < 7) return `${days}d ago`;
+	return new Date(timestamp).toLocaleDateString(undefined, { month: "short", day: "numeric" });
+}