Extract DownloadAssembler service from dashboard routes

- Create server/services/DownloadAssembler.js with 7 pure functions:
  - getCoverArt, getImportIssues, getSonarrLink, getRadarrLink
  - canBlocklist, extractEpisode, gatherEpisodes
- Update server/routes/dashboard.js to use DownloadAssembler
- Add comprehensive unit tests (73 tests covering edge cases)
- Fix null check in extractEpisode function
- All tests passing: DownloadAssembler (73/73), TagMatcher (26/26)

server/services/DownloadAssembler.js

@@ -0,0 +1,107 @@
+// Copyright (c) 2026 Gordon Bolton. MIT License.
+
+// Helper function to extract poster/cover art URL from a movie or series object
+function getCoverArt(item) {
+  if (!item || !item.images) return null;
+  const poster = item.images.find(img => img.coverType === 'poster');
+  if (poster) return poster.remoteUrl || poster.url || null;
+  // Fallback to fanart if no poster
+  const fanart = item.images.find(img => img.coverType === 'fanart');
+  return fanart ? (fanart.remoteUrl || fanart.url || null) : null;
+}
+
+// Extract import issues from a Sonarr/Radarr queue record
+function getImportIssues(queueRecord) {
+  if (!queueRecord) return null;
+  const state = queueRecord.trackedDownloadState;
+  const status = queueRecord.trackedDownloadStatus;
+  if (state !== 'importPending' && status !== 'warning' && status !== 'error') return null;
+  const messages = [];
+  if (queueRecord.statusMessages && queueRecord.statusMessages.length > 0) {
+    for (const sm of queueRecord.statusMessages) {
+      if (sm.messages && sm.messages.length > 0) {
+        messages.push(...sm.messages);
+      } else if (sm.title) {
+        messages.push(sm.title);
+      }
+    }
+  }
+  if (queueRecord.errorMessage) {
+    messages.push(queueRecord.errorMessage);
+  }
+  if (messages.length === 0) return null;
+  return messages;
+}
+
+// Helper to build Sonarr web UI link for a series
+function getSonarrLink(series) {
+  if (!series || !series._instanceUrl || !series.titleSlug) return null;
+  return `${series._instanceUrl}/series/${series.titleSlug}`;
+}
+
+// Helper to build Radarr web UI link for a movie
+function getRadarrLink(movie) {
+  if (!movie || !movie._instanceUrl || !movie.titleSlug) return null;
+  return `${movie._instanceUrl}/movie/${movie.titleSlug}`;
+}
+
+// Determine if a download can be blocklisted by the current user
+// Admins: always true (they have arrQueueId)
+// Non-admins: true if importIssues OR (torrent >1h old AND availability<100%)
+function canBlocklist(download, isAdmin) {
+  if (isAdmin) return true;
+  if (download.importIssues && download.importIssues.length > 0) return true;
+  if (download.qbittorrent && download.addedOn && download.availability) {
+    const oneHourAgo = Date.now() - 3600000; // 1 hour in ms
+    const addedOn = new Date(download.addedOn).getTime();
+    const isOldEnough = addedOn < oneHourAgo;
+    const availability = parseFloat(download.availability);
+    const isLowAvailability = availability < 100;
+    return isOldEnough && isLowAvailability;
+  }
+  return false;
+}
+
+// Extract episode info from a Sonarr queue/history record.
+// Returns { season, episode, title } or null if data is missing.
+function extractEpisode(record) {
+  if (!record) return null;
+  const ep = record.episode || {};
+  const s = ep.seasonNumber != null ? ep.seasonNumber : record.seasonNumber;
+  const e = ep.episodeNumber != null ? ep.episodeNumber : record.episodeNumber;
+  if (s == null || e == null) return null;
+  const title = ep.title || null;
+  return { season: s, episode: e, title };
+}
+
+// Find all episodes associated with a download by matching all queue/history records
+// that share the same title string.  Returns sorted array of { season, episode, title }.
+function gatherEpisodes(titleLower, sonarrRecords) {
+  const episodes = [];
+  const seen = new Set();
+  for (const r of sonarrRecords) {
+    const rTitle = (r.title || r.sourceTitle || '').toLowerCase();
+    if (rTitle && (rTitle.includes(titleLower) || titleLower.includes(rTitle))) {
+      const ep = extractEpisode(r);
+      if (ep) {
+        const key = `${ep.season}x${ep.episode}`;
+        if (!seen.has(key)) {
+          seen.add(key);
+          episodes.push(ep);
+        }
+      }
+    }
+  }
+  episodes.sort((a, b) => a.season - b.season || a.episode - b.episode);
+  return episodes;
+}
+
+module.exports = {
+  getCoverArt,
+  getImportIssues,
+  getSonarrLink,
+  getRadarrLink,
+  canBlocklist,
+  extractEpisode,
+  gatherEpisodes
+};