Add comprehensive approval queue architecture research and migration strategy

Research project evaluating replacement of file-based approval queue with
distributed message broker (Redis vs RabbitMQ) for TeaAgent.

Research Documents:
- approval-queue-security-assessment-2026-06-10.md: Security analysis of
  networked queue architecture, attack surface evaluation, and security
  control requirements
- approval-queue-dependency-evaluation-2026-06-10.md: Redis vs RabbitMQ
  comparison covering operational complexity, team expertise, TCO analysis
- approval-queue-performance-comparison-2026-06-10.md: Performance
  benchmarking results comparing file-based vs Redis implementations
- approval-queue-migration-strategy-2026-06-10.md: 5-phase migration plan
  with hybrid architecture, dual-write strategy, and rollback procedures

Benchmark Scripts:
- benchmark_approval_queue.py: File-based queue performance benchmark
- benchmark_redis_approval_queue.py: Redis queue performance benchmark

Benchmark Results:
- approval_queue_benchmark_results.json: File-based baseline metrics
- redis_approval_queue_benchmark_results.json: Redis performance metrics

Key Findings:
- Redis batch approval: 3-35x faster (solves critical 5+ second latency)
- File-based reads: 100-1000x faster than Redis reads
- Recommended: Hybrid architecture (file-based reads + Redis writes)
- Migration: 5-week timeline with zero downtime and 5-minute rollback

Constraint: Research-only deliverables, no production code changes
Tested: Benchmark scripts executed successfully with both file-based and Redis implementations
Confidence: high

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Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

Author: johnteee