Add livekit-agents-production skill for existing codebases

[rathoresids]

What does this PR do?

Adds a new skill (livekit-agents-production) focused on extending, debugging, and operating existing LiveKit agent codebases. This complements the existing livekit-agents skill (which covers building from scratch) with production-stage guidance.

The new skill covers:

• Worker process model — parent-child architecture, shared state inheritance, and async context implications
• Safe async patterns — avoiding the most common class of production bugs (event loop conflicts in worker processes)
• Provider lifecycle — prewarming strategies, cold-start mitigation, failure handling
• Testing within existing infrastructure — using established fixtures, mocking at boundaries, async test patterns
• Performance profiling — what to measure (time-to-first-audio, tool execution, context growth) and common anti-patterns
• Production operations — graceful shutdown, SDK upgrade strategy, observability, debugging common failures

Addresses #6

Design decisions

• Separate skill, not a rewrite — keeps each skill focused: livekit-agents for building, livekit-agents-production for extending and operating
• No code examples — all patterns described as behavioral principles per the "freeze forever" principle
• Not Python-specific — worker model and async patterns framed universally, applicable to both Python and Node SDKs
• 258 lines — well under the 500-line limit

Checklist

• Content passes the "freeze forever" test — would it still be correct if never updated?
• API specifics are directed to MCP/docs, not hardcoded in skill content
• Skill stays under 500 lines
• Trigger phrases in skill description are clear and representative
• Tested with an AI coding agent to verify the skill produces correct behavior

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