feat: queue UX (Phase M) + media editing (split-chapters, trim)

Phase L (media editing):
- Split by chapters (--split-chapters) as a DownloadOptions toggle
- Trim/cut by time range: parseTrimSections -> --download-sections "*A-B"
  + --force-keyframes-at-cuts (deduped vs SponsorBlock), per-download Trim panel

Phase M (queue & daily-use UX), all 7:
- Pause/resume: main-side killTree + paused flag (silent close), download:pause
  IPC, store pause/resume + paused status, QueueItem controls
- Reorder via "Download next" (prioritize)
- Aggregate progress strip (pure summarizeQueue) + combined speed/ETA
- Drag-and-drop links / .url files onto the download card
- Retry all failed
- Duplicate detection (sameVideo) with "Download anyway" guard
- Per-download scheduling (datetime-local) + save-for-later (saved status,
  15s promotion ticker); session-only (queue not persisted)

New pure modules unit-tested (queueStats); buildArgs trim/split tested.
typecheck + test green (178 passed). Roadmap updated: Phase M COMPLETE.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/main/buildArgs.ts

@@ -161,6 +161,30 @@ export function selectExtraArgs(params: {
   return []
 }
 
+/**
+ * Parse a raw trim string (one or more time ranges, comma- or newline-separated)
+ * into yt-dlp `--download-sections` specs. Each range is normalised to the
+ * `*START-END` time-range form yt-dlp expects (the leading `*` distinguishes a
+ * timestamp range from a chapter-title regex). Tokens that don't look like a
+ * numeric time range are dropped, so malformed input can't reach yt-dlp's argv.
+ *
+ * Accepts H:MM:SS / M:SS / SS with optional fractional seconds, e.g. '1:30-2:00',
+ * '90-120', '0:00:10.5-0:00:20'. A token may already carry the leading `*`.
+ */
+export function parseTrimSections(raw: string | undefined): string[] {
+  if (!raw) return []
+  const TIME = String.raw`\d+(?::\d{1,2})*(?:\.\d+)?`
+  const RANGE = new RegExp(`^${TIME}-${TIME}$`)
+  const out: string[] = []
+  for (const piece of raw.split(/[,\n]/)) {
+    let t = piece.trim()
+    if (!t) continue
+    if (t.startsWith('*')) t = t.slice(1).trim()
+    if (RANGE.test(t)) out.push(`*${t}`)
+  }
+  return out
+}
+
 // Wrap a single argv token for human-readable display only (Phase C command
 // preview) — never used to build the real argv that gets spawned.
 function quoteForDisplay(arg: string): string {
@@ -250,17 +274,30 @@ function postProcessArgs(opts: StartDownloadOptions, o: DownloadOptions): string
   }
 
   // SponsorBlock.
+  let forcedKeyframes = false
   if (o.sponsorBlock && o.sponsorBlockCategories.length > 0) {
     const cats = o.sponsorBlockCategories.join(',')
     if (o.sponsorBlockMode === 'remove') {
       // Force keyframes at the cut points so segment boundaries are frame-accurate.
       args.push('--sponsorblock-remove', cats, '--force-keyframes-at-cuts')
+      forcedKeyframes = true
     } else {
       args.push('--sponsorblock-mark', cats)
     }
   }
 
+  // Trim — download only the given time ranges (works for video + audio). Force
+  // keyframes at the cut points for frame-accurate boundaries, unless
+  // SponsorBlock-remove already requested it (the flag is idempotent, but we
+  // avoid emitting it twice).
+  const sections = parseTrimSections(opts.trim)
+  for (const sec of sections) args.push('--download-sections', sec)
+  if (sections.length > 0 && !forcedKeyframes) args.push('--force-keyframes-at-cuts')
+
   if (o.embedChapters) args.push('--embed-chapters')
+  // Split into one file per chapter. yt-dlp also keeps the full file; the
+  // per-chapter files use yt-dlp's default `chapter:` output template.
+  if (o.splitChapters) args.push('--split-chapters')
   if (o.embedMetadata) args.push('--embed-metadata')
 
   // Media-server sidecar files (Phase K) — written next to the output file so