ActionCheese Sync 0.2.0

Free, open-source multicam sync for Premiere and DaVinci Resolve. Aligns
footage by its sound, so cameras whose clocks were never set still land
together.

Adding footage is quicker

• Pick several camera folders in one go, instead of one trip through the
  dialog per camera.
• The folder dialog opens where the last one left off — on the shoot, so the
  next camera is a click away rather than a walk back down the tree.
• Merge combines folders for one camera that filled several cards. This
  matters beyond tidiness: clips from one device are never matched against
  each other, on the principle that a camera cannot record two things at
  once, and that has to hold across the card boundary too. Split undoes
  it. On the command line, --merge.

Fixed

• The in-app Help said the app was unsigned. Downloads are signed and
  notarized; only a build you make yourself needs right-click → Open.
• Timelines exported on Windows are now read and written correctly. Their
  media paths arrive in a different shape, and the old handling turned every
  clip into a missing file while writing an XML that relinked nothing. Not
  visible on macOS, but it is the groundwork for a Windows build.

Groundwork

• The code is now cross-platform and its tests pass as such. Windows
  packaging is written but has never been run — see
  docs/PORTING-WINDOWS-LINUX.md.
• docs/ROADMAP.md records what is planned, what each item needs before it
  can be verified, and what is deliberately not planned.

Requirements: Apple silicon Mac, macOS 11 or later. Intel Macs are not
supported. ffmpeg is bundled, so nothing else to install.

297 tests pass.