docs: add proposal for real-time AI agent architecture based on LiveKit

[mitkury]

Explored the LiveKit Agents-JS package to analyze how it manages real-time AI voice/video agents. Extracted key patterns including node-based processing (STT, LLM, TTS), turn detection/interruption logic, and Web Streams integration for asynchronous generation. Drafted a comprehensive proposal in src/proposal.md detailing how these architectures can be referenced or adapted for our own agent development.

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PR created automatically by Jules for task 8429588336330085104 started by @mitkury

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