feat: terminal-native torrent discovery TUI

Curated, multi-source torrent search and download from the terminal:
concurrent search across built-in sources with streamed, source-tagged
results; a download-only webtorrent engine with true pause/resume and
restart recovery; magnet paste; and a calm Ink + React TUI. No indexer
server, no setup.

src/ui/move.ts

@@ -0,0 +1,10 @@
+export function wrapStep(current: number, delta: number, length: number): number {
+  if (length <= 0) return 0;
+  return (((current + delta) % length) + length) % length;
+}
+
+export function windowStart(cursor: number, total: number, height: number): number {
+  if (total <= height) return 0;
+  const half = Math.floor(height / 2);
+  return Math.max(0, Math.min(cursor - half, total - height));
+}