test: add AgentOrchestrator unit tests

Add comprehensive test coverage for AgentOrchestrator.ts (912 lines):
- Initialization tests (dependencies, double-init prevention)
- Turn processing tests (GMI creation, streaming, context)
- Tool calling tests (iteration limits, result processing)
- State management tests (concurrent streams, isolation)
- Shutdown tests (cleanup, reinitialization)

21 test cases covering critical orchestration paths.

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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: jddunn