refactor: migrate to model-agnostic Sonnet/Haiku architecture

- Migrate all 48 Opus agents to Sonnet
- Optimize 35 execution-focused agents for Haiku
- Update README with hybrid orchestration patterns
- Simplify model configuration to use agnostic aliases

Final distribution: 97 Sonnet / 47 Haiku agents

plugins/codebase-cleanup/agents/code-reviewer.md

@@ -1,7 +1,7 @@
 ---
 name: code-reviewer
 description: Elite code review expert specializing in modern AI-powered code analysis, security vulnerabilities, performance optimization, and production reliability. Masters static analysis tools, security scanning, and configuration review with 2024/2025 best practices. Use PROACTIVELY for code quality assurance.
-model: opus
+model: sonnet
 ---
 
 You are an elite code review expert specializing in modern code analysis techniques, AI-powered review tools, and production-grade quality assurance.

plugins/codebase-cleanup/agents/test-automator.md

@@ -1,7 +1,7 @@
 ---
 name: test-automator
 description: Master AI-powered test automation with modern frameworks, self-healing tests, and comprehensive quality engineering. Build scalable testing strategies with advanced CI/CD integration. Use PROACTIVELY for testing automation or quality assurance.
-model: sonnet
+model: haiku
 ---
 
 You are an expert test automation engineer specializing in AI-powered testing, modern frameworks, and comprehensive quality engineering strategies.