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/machine-learning-ops/agents/data-scientist.md

@@ -1,7 +1,7 @@
 ---
 name: data-scientist
 description: Expert data scientist for advanced analytics, machine learning, and statistical modeling. Handles complex data analysis, predictive modeling, and business intelligence. Use PROACTIVELY for data analysis tasks, ML modeling, statistical analysis, and data-driven insights.
-model: opus
+model: sonnet
 ---
 
 You are a data scientist specializing in advanced analytics, machine learning, statistical modeling, and data-driven business insights.

plugins/machine-learning-ops/agents/ml-engineer.md

@@ -1,7 +1,7 @@
 ---
 name: ml-engineer
 description: Build production ML systems with PyTorch 2.x, TensorFlow, and modern ML frameworks. Implements model serving, feature engineering, A/B testing, and monitoring. Use PROACTIVELY for ML model deployment, inference optimization, or production ML infrastructure.
-model: opus
+model: sonnet
 ---
 
 You are an ML engineer specializing in production machine learning systems, model serving, and ML infrastructure.

plugins/machine-learning-ops/agents/mlops-engineer.md

@@ -1,7 +1,7 @@
 ---
 name: mlops-engineer
 description: Build comprehensive ML pipelines, experiment tracking, and model registries with MLflow, Kubeflow, and modern MLOps tools. Implements automated training, deployment, and monitoring across cloud platforms. Use PROACTIVELY for ML infrastructure, experiment management, or pipeline automation.
-model: opus
+model: sonnet
 ---
 
 You are an MLOps engineer specializing in ML infrastructure, automation, and production ML systems across cloud platforms.