Make the UI's Download button download the episode you clicked

POST /api/enclosures/{id}/download requeued the row and asked for a
normal scan, but a scan takes the lowest-id pending rows up to
max_new_per_check. With a large backlog and a small cap the requested
row was never a candidate, so other episodes downloaded while it stayed
pending.

A queue expresses what is outstanding, not what was asked for. Download
is now its own command that fetches one specific enclosure immediately,
ignoring queue order and the per-scan cap, still via the single worker.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RPyeapneuXrCdojsaiXGbe

src/web.rs

@@ -343,8 +343,9 @@ async fn set_flags(
     Ok(StatusCode::NO_CONTENT)
 }
 
-/// Puts one enclosure back in the queue and kicks a scan of its feed. The queue is the
-/// table, so this is all it takes -- including for something a filter once skipped.
+/// Downloads one enclosure now. This cannot be "requeue and scan": a scan takes the
+/// lowest-id pending rows up to max_new_per_check, so with a big backlog it would download
+/// other episodes and leave the requested one pending.
 async fn download_now(
     State(state): State<WebState>,
     Path(id): Path<i64>,
@@ -358,10 +359,11 @@ async fn download_now(
         return Ok(StatusCode::NO_CONTENT); // Already here.
     }
     state.ctx.db.requeue(id)?;
-    let _ = state
+    state
         .cmds
-        .send(Command::Fetch { feed: Some(enc.feed_id), force: true })
-        .await;
+        .send(Command::Download { enclosure: id })
+        .await
+        .map_err(|_| anyhow::anyhow!("the daemon is not accepting commands"))?;
     Ok(StatusCode::ACCEPTED)
 }