feat: media and image support

[dodaa08]

Media & Image Support

• Attachment classification — extracts and categorizes attached files (image, audio, video, document, or unknown) from Rocket.Chat messages, handling both uploaded files and URL-based attachments

• File download materialization — downloads private/local-hosted attachments (blocked by SSRF otherwise) to a local temp directory before passing them to the agent, so image analysis works without external URLs

• File upload to Rocket.Chat — sends files back from the agent to Rocket.Chat rooms with thread support

• Agent media context — private URLs are injected as MediaPath (local file), public URLs passthrough as MediaUrl, with MIME type info so the agent knows what it's looking at

• Attachment-aware message handling — messages with only attachments and no text are no longer skipped; outbound replies with files use the upload path instead of plain text

• Config — added vision-capable models (Llama 3.2 Vision, Phi-4 Multimodal) with input: ["text", "image"] and an imageModel agent default