feat(pinchflat): Retention & quality-upgrade per Library source

On-demand maintenance panel (SourceRetention) on the source detail —
not a persisted schedule (roadmap's niche-for-desktop scope).

Prune: keep the newest N downloaded files, delete the rest's files
(download archive prevents silent re-download); dry-run count + two-step
confirm before any deletion. Upgrade: re-enqueue items whose recorded
downloadedQuality ranks below the source's current target (profile or
global). Selection is pure + injected-now in @shared/retention.ts
(selectPruneCandidates/selectUpgradeCandidates + qualityRank), unit-
tested; pruneMediaItems (main) deletes best-effort and clears state.
MediaItem.downloadedQuality now recorded through the completion path.
Live-verified the panel renders. 366 tests pass.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/main/sources.ts

@@ -12,6 +12,7 @@
  * can't feed the UI malformed records (same approach as history/errorlog).
  */
 
+import { existsSync, unlinkSync } from 'fs'
 import type { Source, MediaItem } from '@shared/ipc'
 import { isValidSource, isValidMediaItem } from './core/validation'
 import { mergeItemsPreservingState } from './core/indexerCore'
@@ -115,13 +116,54 @@ export function mergeMediaItems(
  * updated list for that item's source (or [] if the id is unknown). Used by the
  * library view once a queued item completes (Phase H/I).
  */
-export function setMediaItemDownloaded(id: string, filePath?: string): MediaItem[] {
+export function setMediaItemDownloaded(
+  id: string,
+  filePath?: string,
+  quality?: string
+): MediaItem[] {
   const all = listAllItems()
   const target = all.find((m) => m.id === id)
   if (!target) return []
   const updated = all.map((m) =>
-    m.id === id ? { ...m, downloaded: true, downloadedAt: Date.now(), filePath } : m
+    m.id === id
+      ? { ...m, downloaded: true, downloadedAt: Date.now(), filePath, downloadedQuality: quality }
+      : m
   )
   itemsStore.write(updated)
   return updated.filter((m) => m.sourceId === target.sourceId)
 }
+
+/**
+ * Prune (delete the files of) the given media items for a source, then clear
+ * their downloaded state so the Library shows them as pending again. The
+ * download-archive guard (Settings.useDownloadArchive) keeps a pruned video from
+ * silently re-downloading on the next "Download new only". Returns the updated
+ * item list for the source and how many files were actually deleted.
+ *
+ * File deletion is the caller's explicit, dry-run-confirmed action (the source
+ * detail's Prune button) — never automatic.
+ */
+export function pruneMediaItems(
+  sourceId: string,
+  itemIds: string[]
+): { items: MediaItem[]; deleted: number } {
+  const remove = new Set(itemIds)
+  const all = listAllItems()
+  let deleted = 0
+  const updated = all.map((m) => {
+    if (!remove.has(m.id)) return m
+    if (m.filePath && existsSync(m.filePath)) {
+      try {
+        unlinkSync(m.filePath)
+        deleted++
+      } catch {
+        /* best-effort — a locked/already-gone file just stays counted as not-deleted */
+      }
+    }
+    // Clear the on-disk state; the download archive prevents a silent re-download.
+    const { filePath: _f, downloadedAt: _a, downloadedQuality: _q, ...rest } = m
+    return { ...rest, downloaded: false }
+  })
+  itemsStore.write(updated)
+  return { items: updated.filter((m) => m.sourceId === sourceId), deleted }
+}