greetd only launches the session after the greeter process exits. Quit
on successful StartSession instead of sitting on "Starting session…"
until SIGTERM.
Empty Secret/Visible answers are Some("") (not PAM cancel). The greetd
actor stays up across connect failure and reconnects. Escape cancels
the conversation. Session env sets XDG_SESSION_TYPE/DESKTOP. .desktop
parsing honors Hidden/NoDisplay/TryExec and quoted Exec=. Invalid TOML
warns instead of failing silent. Font, date, and Ken Burns config match
what the greeter actually draws.
List .desktop sessions from the existing scan, pre-select bos when
present (else the first entry), and pass the chosen Exec= argv to
greetd StartSession.
