PLAY turns into UPDATE CLIENT when a tracked client is outdated; with no client linked
it offers choosing an existing folder or downloading from the community launcher servers
(resumable, hash-verified, free-space checked, progress and stop). Files the player changed
are kept on request or moved aside, never silently replaced. Existing clients can be adopted
from Settings. Fresh downloads get a realmlist for each installed locale.
Fixes zero-length files in the downloader (found by the live probe).
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Verified in the native window against a disposable fixture: import writes only
<folder>.manager + registry; start surfaces a human 'database update required'
message; stop returns to Offline. Live install untouched throughout.
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>