bin/quak.ts: commander-based CLI with login (interactive + QUAK_EMAIL/
QUAK_PASSWORD env vars), whoami, logout, backup commands. Session
stored at env-paths('quak').data/session.json (~/Library/Application
Support/quak/ on macOS, XDG on Linux).
src/backup.ts: runBackup downloads all files into originals/<id>.<ext>,
symlinks into collections/<name>/<title>, writes per-collection JSON
metadata at collections/<name>.json. Deduplicates across collections
(each file downloaded once). Skips existing originals on incremental
runs. Never crashes on single-file failure.
4 backup tests + live-tested against real Ente account.
