feat(mistral-ai): update model YAMLs [bot]

[harshiv-26]

Auto-generated by poc-agent for provider mistral-ai.

---

Note

Low Risk
Config-only YAML metadata changes with limited blast radius; primary risk is mislabeling modalities/provisioning affecting model selection or routing.

Overview
Updates Mistral model definitions for voxtral-mini-realtime-2602 and voxtral-mini-tts-2603 by adding explicit modalities (audio→text for realtime transcribe; text→audio for TTS) and marking both models as provisioning: serverless.

Also removes an extra/outdated documentation source link from the realtime model’s sources list.

^{Reviewed by Cursor Bugbot for commit 627370b. Bugbot is set up for automated code reviews on this repo. Configure here.}