Play and delete a torrent that came as a folder of files (#158)

A torrent of several files is recorded as its folder. /media could not serve a folder, and the
reaper's remove_file failed on it, warned "could not delete" on every pass and freed nothing, so it
counted against the quota for good; Delete in the page failed the same way.

download::remove deletes a file or a whole folder, for the reaper and Delete alike, and the reaper
counts a folder by its recorded size, as a directory's own size is not its contents'.
download::playable answers the path itself, or for a folder the largest file in it, which is the
episode, and /media serves that.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/retention.rs

@@ -96,9 +96,13 @@ async fn remove(db: &Db, c: &Candidate, dry_run: bool) -> Result<u64> {
     if dry_run {
         return Ok(c.bytes.max(0) as u64);
     }
-    let size = std::fs::metadata(&c.path).map(|m| m.len()).unwrap_or(c.bytes.max(0) as u64);
+    // A torrent's folder measures as a directory entry, not what is in it: the recorded size then.
+    let size = std::fs::metadata(&c.path)
+        .ok()
+        .filter(|m| m.is_file())
+        .map_or(c.bytes.max(0) as u64, |m| m.len());
     // Missing is fine: the point is that it is gone.
-    if let Err(e) = std::fs::remove_file(&c.path)
+    if let Err(e) = crate::download::remove(std::path::Path::new(&c.path))
         && e.kind() != std::io::ErrorKind::NotFound
     {
         tracing::warn!(path = c.path, error = %e, "could not delete");