Remove sys.excepthook that unlocked on crash — this violated
ext-session-lock-v1 security model where the compositor must keep
the screen locked if the client dies (per protocol spec and hyprlock
reference). Now: crashes are logged but session stays locked.
SIGUSR1 handler added for external recovery (e.g. wrapper script).
Global sys.excepthook unlocks the session on unhandled exceptions.
Structured logging to stderr and optional file at /var/cache/moonlock/.
Window creation, CSS loading, and fingerprint start wrapped in
try/except with automatic session unlock when all windows fail.
