* feat(fal_ai): add Nano Banana / Gemini 2.5 Flash Image generation support
Adds a FalAINanoBananaConfig for fal.ai's Nano Banana models, exposed under
both fal-ai/nano-banana and fal-ai/gemini-25-flash-image (identical schema).
This is the migration path for fal-ai/imagen4, which fal deprecates on
2026-06-30.
The config derives the request endpoint from the model name so both aliases
route correctly, maps OpenAI image params to the fal schema (n -> num_images,
size -> nearest supported aspect_ratio, response_format ignored since the model
returns URLs), and reuses the base fal response parser. Pricing is registered
at 0.039 per image in the cost map and backup.
* fix(fal_ai): tighten nano-banana routing and guard mapped params
Match the specific gemini-25-flash-image / gemini-2.5-flash-image
aliases instead of any model containing gemini so future fal.ai
Gemini-branded models aren't silently misrouted to the nano-banana
config. Guard the param mapping on the fal-side keys (num_images,
aspect_ratio) so a pre-set mapped value is respected and an OpenAI
key is never forwarded unmapped.
* fix(fal_ai): drop non-existent gemini-2.5-flash-image routing alias
fal.ai only serves the dotted-free fal-ai/gemini-25-flash-image and
fal-ai/nano-banana endpoints. Routing the dotted gemini-2.5-flash-image
alias built a https://fal.run/fal-ai/gemini-2.5-flash-image URL that
fal.ai 404s and had no pricing entry, so spend tracking silently fell to
zero. Match only the two real endpoint slugs.
51769a8ede