Further reduce supervisor and runtime debt

[hawkli-1994]

Summary

• extract conversation route registration out of supervisor.py into a dedicated router module
• move DeerFlow runtime event processing helpers out of general_agent.py
• extract front-end NDJSON stream parsing and scroll helpers from v0-ai-chat.tsx

Validation

• uv run ruff check swarmmind tests
• cd ui && pnpm exec tsc --noEmit
• make test

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