- toast-fragment.php: 204 early-exit now also checks flash['warning'];
previously the warning was consumed by consumeFlash() then silently dropped
- partage/index.php: store warning as plain text; htmlspecialchars() applied
once at render time — previously htmlspecialchars() was called inside the
stored string then again at output, producing ' entities etc.
- partage/index.php: flash-warning div gets id + tabindex=-1; inline JS
scrolls it into view and focuses it on DOMContentLoaded
- admin/footer.php: htmx:afterSettle listener focuses .toast--warning after
HTMX injects the toast fragment into #toast-region
