docs(architecture): add realtime-pipeline design doc for low-latency meeting streaming

[cto-new]

Summary

This PR adds a comprehensive design document detailing a low-latency realtime meeting streaming pipeline. It captures ingestion, buffering/windowing, parallel ASR/translation/TTS, voice cloning synthesis, music remixing, and delivery, with explicit streaming protocols, backpressure, GPU scheduling, and a sub-2s end-to-end target for 1000+ concurrent sessions.

Details

• Created docs/architecture/realtime-pipeline.md outlining the architecture, data flow, buffering strategy, async messaging, streaming protocols, backpressure handling, GPU scheduling, voice cloning, music remixing, and delivery.
• Included sequence diagrams and resource estimates for 1000+ concurrent sessions.
• Documented acceptance criteria coverage: buffering strategy, async messaging, failure handling, and monitoring hooks.
• Added repository scaffolding: docs/architecture directory and .gitignore to standardize project structure.

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