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>

test/buildArgs.test.ts

@@ -2,6 +2,7 @@ import { describe, it, expect } from 'vitest'
 import {
   buildArgs,
   parseExtraArgs,
+  parseTrimSections,
   selectExtraArgs,
   formatCommandLine,
   sanitizeDirSegment,
@@ -460,6 +461,71 @@ describe('sidecar files', () => {
   })
 })
 
+describe('chapters', () => {
+  it('emits --split-chapters when splitChapters is on', () => {
+    expect(build(opts(), dlo({ splitChapters: true }))).toContain('--split-chapters')
+  })
+
+  it('does not emit --split-chapters by default', () => {
+    expect(build(opts(), dlo())).not.toContain('--split-chapters')
+  })
+
+  it('emits --split-chapters independently of --embed-chapters', () => {
+    const argv = build(opts(), dlo({ splitChapters: true, embedChapters: false }))
+    expect(argv).toContain('--split-chapters')
+    expect(argv).not.toContain('--embed-chapters')
+  })
+})
+
+describe('parseTrimSections', () => {
+  it('normalises plain time ranges to *START-END specs', () => {
+    expect(parseTrimSections('1:30-2:00')).toEqual(['*1:30-2:00'])
+    expect(parseTrimSections('90-120')).toEqual(['*90-120'])
+    expect(parseTrimSections('0:00:10.5-0:00:20')).toEqual(['*0:00:10.5-0:00:20'])
+  })
+
+  it('splits on commas and newlines and trims whitespace', () => {
+    expect(parseTrimSections(' 0:30-1:00 , 2:00-2:30 \n 3:00-3:30 ')).toEqual([
+      '*0:30-1:00',
+      '*2:00-2:30',
+      '*3:00-3:30'
+    ])
+  })
+
+  it('keeps an existing leading * but does not double it', () => {
+    expect(parseTrimSections('*1:00-2:00')).toEqual(['*1:00-2:00'])
+  })
+
+  it('drops malformed tokens so garbage never reaches the argv', () => {
+    expect(parseTrimSections('not-a-range')).toEqual([])
+    expect(parseTrimSections('1:30')).toEqual([]) // no end
+    expect(parseTrimSections('')).toEqual([])
+    expect(parseTrimSections(undefined)).toEqual([])
+  })
+})
+
+describe('trim (--download-sections)', () => {
+  it('emits a --download-sections spec per range plus --force-keyframes-at-cuts', () => {
+    const argv = build(opts({ trim: '0:30-1:00, 2:00-2:30' }), dlo())
+    expect(hasSeq(argv, '--download-sections', '*0:30-1:00')).toBe(true)
+    expect(hasSeq(argv, '--download-sections', '*2:00-2:30')).toBe(true)
+    expect(argv).toContain('--force-keyframes-at-cuts')
+  })
+
+  it('emits nothing when there is no trim', () => {
+    const argv = build(opts(), dlo())
+    expect(argv).not.toContain('--download-sections')
+  })
+
+  it('does not double --force-keyframes-at-cuts when SponsorBlock-remove is also on', () => {
+    const argv = build(
+      opts({ trim: '0:30-1:00' }),
+      dlo({ sponsorBlock: true, sponsorBlockMode: 'remove', sponsorBlockCategories: ['sponsor'] })
+    )
+    expect(argv.filter((a) => a === '--force-keyframes-at-cuts')).toHaveLength(1)
+  })
+})
+
 // --- Collection folder paths (Phase G, media-manager) -----------------------
 
 describe('sanitizeDirSegment', () => {