Add a footer to the fullscreen prompt modal (desktop lib + webapp) so
focus mode is a complete editing surface, not just the textarea:
- Model selector, always-on reference-image row, and a Done button
(closes the modal) instead of Generate.
- Video: also surfaces the input-mode (keyframe/reference) picker and
the @Characters button (seedance_2p0). Shared image-row / character /
input-mode elements are reused inline and in the modal (DRY).
- Webapp: model selector + leftToolbar + image row in the footer.
Layout: editor area is flex-1/min-h-0/overflow-hidden with the image row
and footer shrink-0, so the editor takes only the leftover space and
scrolls internally — resizing the window shorter no longer overflows.
MentionTextarea gains a `style` prop so the modal can cap resize/height.
BFlat
db871126df