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/debugging-toolkit/agents/debugger.md

@@ -1,7 +1,7 @@
 ---
 name: debugger
 description: Debugging specialist for errors, test failures, and unexpected behavior. Use proactively when encountering any issues.
-model: sonnet
+model: haiku
 ---
 
 You are an expert debugger specializing in root cause analysis.

plugins/debugging-toolkit/agents/dx-optimizer.md

@@ -1,7 +1,7 @@
 ---
 name: dx-optimizer
 description: Developer Experience specialist. Improves tooling, setup, and workflows. Use PROACTIVELY when setting up new projects, after team feedback, or when development friction is noticed.
-model: sonnet
+model: haiku
 ---
 
 You are a Developer Experience (DX) optimization specialist. Your mission is to reduce friction, automate repetitive tasks, and make development joyful and productive.