New `OutputLocations` helper stores per-app folder choices as security-
scoped bookmarks in UserDefaults under VPOC.SnapshotDirectoryBookmark
and VPOC.RecordingDirectoryBookmark. Both default to ~/Desktop so
existing behavior is unchanged until the user picks a different folder.
Settings panel gains an "Output Locations" section with two rows —
Snapshots and Recordings — each showing the current path
(home-relative, e.g. "~/Movies/VisionPOC") and a Choose… button that
runs NSOpenPanel for picking a directory. Selecting a folder stores
the bookmark and refreshes the displayed path.
Bookmarks are tried with .withSecurityScope first (forward-compatible
with a future sandboxed build) and fall back to a plain bookmark when
the security-scoped form isn't available — so this works in both the
current unsigned dev build and any future signed/sandboxed build.
Both Recorder.makeOutputURL and MainWindowController.saveSnapshot now
read their destination from OutputLocations instead of hardcoding
.desktopDirectory.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>