Follow-up fixes for the #3775 audit findings:
- Bill Grok video generation per second of output, matching the xAI rate
card: parse the request duration (1-15s, upstream default 8s) and compute
cost as per-second price x duration x count. The built-in rate card values
were already xAI per-second prices but were previously charged per video,
undercharging up to 15x with a user-controlled duration.
- Group video_price_* fields are now documented and surfaced as per-second
rates (USD/s); admin UI labels, placeholders and hints updated accordingly.
- Persist video_count/video_resolution/video_duration_seconds on usage_logs
(migration 172) so video billing is auditable, and exempt any row with
video_count > 0 from the image_size check constraint: a video billed via a
token-mode channel price produces billing_mode='token' with image_count=1
and no image_size, which the previous constraint rejected, dropping the
whole billing transaction.
- Only refetch the group in apiKeyWithFreshGroupMediaPricing when the group
object actually looks like it is missing media pricing fields (both media
multipliers zero and all prices nil, impossible for a normally loaded
group), removing a per-usage DB query for groups without overrides.
- Frontend: drop the unused admin.groups.mediaPricing locale block, map
cleared price inputs to null (create) / -1 (update, cleared via backend
normalizePrice) instead of sending "" that failed *float64 unmarshalling,
and align video price placeholders with the text-to-video default model
(grok-imagine-video 0.05/0.07, 1080p only on 1.5 at 0.25).
feeeei