feat: download ETA on the press bar from measured Soulseek throughput

Show a live "~Xm left" countdown on the download progress bar. The slskd download
loop already polls byte transfer every 3s; measure the actual throughput (EWMA-
smoothed bytes/sec), compute seconds-remaining from the album's total bytes, and
surface it. New nullable Job.downloadEtaSeconds (migration; web entrypoint runs
prisma migrate deploy), threaded through the on_progress callback (optional 2nd arg,
so other adapters/callers are unaffected — they report no ETA). API exposes it;
queue.tsx renders etaLabel() after the track count. Null when unknown (no sample yet
or a source that doesn't report bytes). Worker 330 tests, web 214 tests, both green;
verified live-rendered as "42% · 6/14 tracks · ~4m left".

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

web/src/app/queue.tsx

@@ -1,7 +1,7 @@
 "use client";
 
 import { useEffect, useState } from "react";
-import { describeJob, timeAgo } from "./_ui/status";
+import { describeJob, etaLabel, timeAgo } from "./_ui/status";
 import { StatTiles } from "./_ui/stat-tiles";
 import { SectionHeader } from "./_ui/section-header";
 import { JobRow } from "./_ui/job-row";
@@ -46,6 +46,7 @@ type Row = {
     candidateCount: number;
     chosen: { source: string; format: string; trackCount: number } | null;
     downloadProgress: number;
+    downloadEtaSeconds: number | null;
     paused: boolean;
   } | null;
 };
@@ -62,6 +63,7 @@ function jobOf(r: Row) {
       candidateCount: 0,
       chosen: null,
       downloadProgress: 0,
+      downloadEtaSeconds: null,
       paused: false,
     }
   );
@@ -270,13 +272,9 @@ export function Queue() {
       } else {
         const total = j.chosen?.trackCount ?? 0;
         const done = total ? Math.round((pct / 100) * total) : 0;
-        bar = (
-          <ProgressBar
-            kind="working"
-            percent={pct}
-            caption={total ? `${pct}% · ${done}/${total} tracks` : `${pct}%`}
-          />
-        );
+        const base = total ? `${pct}% · ${done}/${total} tracks` : `${pct}%`;
+        const eta = etaLabel(j.downloadEtaSeconds);
+        bar = <ProgressBar kind="working" percent={pct} caption={eta ? `${base} · ${eta}` : base} />;
       }
     } else if (j.state === "tagging") {
       bar = <ProgressBar kind="verify" indeterminate caption="finishing" />;