support video inputs in .chat

[P3il4]

added support for video urls, files and base64 in puter.ai.chat
tested:

// just video
puter.ai.chat("What do you see?", "https://rey-assets.puter.site/video.mp4", {model: "reka/reka-edge"})
// just image
puter.ai.chat("What do you see?", "https://rey-assets.puter.site/doge.jpeg", {model: "reka/reka-edge"})
// mixed
puter.ai.chat("Describe these", [
         "https://rey-assets.puter.site/doge.jpeg",
         "https://rey-assets.puter.site/video.mp4",
     ], { model: "reka/reka-edge" })
// another model
puter.ai.chat("Describe these", [
         "https://rey-assets.puter.site/doge.jpeg",
         "https://rey-assets.puter.site/video.mp4",
     ], { model: "google/gemini-2.5-flash" })
// also pass file object or base64

also added a docs entry for video analysis

closes #2733