feat(gallery): add Wan 2.1 FLF2V 14B 720P (#9440)

First-last-frame-to-video variant of the 14B Wan family. Accepts a
start and end reference image and — unlike the pure i2v path — runs
both through clip_vision, so the final frame lands on the end image
both in pixel and semantic space. Right pick for seamless loops
(start_image == end_image) and narrative A→B cuts.

Shares the same VAE, umt5_xxl text encoder, and clip_vision_h as the
I2V 14B entry. Options block mirrors i2v's full-list-in-override
style so the template merge doesn't drop fields.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>