Sessions move from an in-memory map (absolute 12h TTL) to a `sessions`
table (migration 0002), storing only the SHA-256 of the token. Expiry is
now a sliding idle window (PANEL_SESSION_IDLE_DAYS, default 7, no
absolute cap), extended at most once an hour and never by the
monitoring screens' background polling (GET + HX-Request), so a
forgotten open tab doesn't keep a session alive indefinitely. A login
now survives a container restart or redeploy.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
