Inspect fewer files: skip later volumes under random stems

Of 5,000 waiting inspection jobs, 3,212 were queued only because their
stem looked random, and 2,044 of those were later RAR volumes
(xyz.part47.rar, .r00) or par2 recovery volumes (.vol03+04.par2). Their
first segment adds nothing: the set is listed from its first volume and
named from its index .par2, as for readable names already. Each one cost a
~700 KB download; inspection pulled ~85 MB/s and fell behind the backfill.

- isCandidate() rejects later volumes (isLaterVolume) before the random-
  name rule.
- worker:file only queues files that are candidates, so the ~30% that
  inspection skips anyway no longer take queue slots.

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

app/services/ContentService.ts

@@ -8,6 +8,7 @@ import { decodeSegment, YencCrcError, YencError, YencFile } from '#lib/yenc/inde
 import NzbImportService, { type NzbImportResult } from '#services/NzbImportService'
 import {
   isArchiveStart,
+  isLaterVolume,
   NICOVIDEO_FILE,
   NICOVIDEO_RELEASE,
   nicovideoInfo,
@@ -68,6 +69,8 @@ export interface ContentResult {
 class ContentService {
   /** Random or missing names, and named first RAR volumes (for contents and password flag). */
   isCandidate(name: string) {
+    // Even under a random stem: the first volume and the index .par2 are inspected instead.
+    if (isLaterVolume(name)) return false
     if (!looksLikeFilename(name) || looksRandom(fileStem(name))) return true
     if (isArchiveStart(name)) return true
     if (/\.nzb$/i.test(name)) return true