fix veo video with proxy link

[P3il4]

fixes issue where gemini video provider returns link that requires auth to access
now proxied with fileid + access signature
testing:

await puter.ai.txt2vid('A cat walking on a beach at sunset', {"model":"google:google/veo-3.1-lite"})

returns

http://api.puter.localhost:4100
/puterai/video/proxy
?fileId=ttzx0324nd16 <- gemini file download id
&provider=gemini
&expires=1776014720 <- 48h expiration
&signature=18a1491ad9bea510fc57a210a9f6baeeea6560e0fc275d59b7769c6c263e8ad5
^ signature created similarly to other parts of codebase