Log why a track falls back to audio-only

Whether a clip gets a picture is decided by a format lookup whose failure
was only logged at debug, so an audio-only fallback was indistinguishable
from video being broken. The reason is now visible at the default log
level, and taking the video path says so too.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/sources/ytdlp.ts

@@ -363,9 +363,17 @@ export async function hasProgressiveVideo(pageUrl: string, maxHeight: number): P
       "%(format_id)s",
       pageUrl,
     ]);
-    return stdout.trim().length > 0;
+    const formatId = stdout.trim();
+    if (!formatId) {
+      log.warn({ pageUrl }, "no progressive format offered, playing audio only");
+      return false;
+    }
+    log.info({ pageUrl, formatId }, "progressive format for video playback");
+    return true;
   } catch (err) {
-    log.debug({ err, pageUrl }, "no progressive format for video playback");
+    // Worth seeing: this is the difference between "clip plays" and "sound only".
+    const reason = err instanceof Error ? err.message : String(err);
+    log.warn({ pageUrl, reason }, "format lookup failed, playing audio only");
     return false;
   }
 }