Add like count to videos

Same pattern as view_count: model column, yt-dlp extraction, SQL select,
VideoDetail field, startup migration, and display in Watch meta row.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/pages/Watch.jsx

@@ -894,6 +894,7 @@ export default function Watch() {
             <div className="flex items-center gap-2 text-sm text-zinc-500 flex-wrap">
               {date && <span>{date}</span>}
               {video?.view_count > 0 && <><span>·</span><span>{formatViews(video.view_count)}</span></>}
+              {video?.like_count > 0 && <><span>·</span><span>👍 {formatViews(video.like_count).replace(" views", "")}</span></>}
               {video?.category && <><span>·</span><span>{video.category}</span></>}
               {video?.duration_seconds && (
                 <><span>·</span>