feat(skills): restore 60 bundled skills (#42)

* feat(skills): restore ansible skill

* feat(skills): restore api-tester skill

* feat(skills): restore aws skill

* feat(skills): restore azure skill

* feat(skills): restore ci-cd skill

* feat(skills): restore code-reviewer skill

* feat(skills): restore compliance skill

* feat(skills): restore confluence skill

* feat(skills): restore crypto-expert skill

* feat(skills): restore css-expert skill

* feat(skills): restore data-analyst skill

* feat(skills): restore data-pipeline skill

* feat(skills): restore docker skill

* feat(skills): restore elasticsearch skill

* feat(skills): restore email-writer skill

* feat(skills): restore figma-expert skill

* feat(skills): restore gcp skill

* feat(skills): restore git-expert skill

* feat(skills): restore github skill

* feat(skills): restore golang-expert skill

* feat(skills): restore graphql-expert skill

* feat(skills): restore helm skill

* feat(skills): restore interview-prep skill

* feat(skills): restore jira skill

* feat(skills): restore kubernetes skill

* feat(skills): restore linear-tools skill

* feat(skills): restore linux-networking skill

* feat(skills): restore llm-finetuning skill

* feat(skills): restore ml-engineer skill

* feat(skills): restore mongodb skill

* feat(skills): restore nextjs-expert skill

* feat(skills): restore nginx skill

* feat(skills): restore notion skill

* feat(skills): restore oauth-expert skill

* feat(skills): restore openapi-expert skill

* feat(skills): restore pdf-reader skill

* feat(skills): restore postgres-expert skill

* feat(skills): restore presentation skill

* feat(skills): restore project-manager skill

* feat(skills): restore prometheus skill

* feat(skills): restore prompt-engineer skill

* feat(skills): restore python-expert skill

* feat(skills): restore react-expert skill

* feat(skills): restore redis-expert skill

* feat(skills): restore regex-expert skill

* feat(skills): restore rust-expert skill

* feat(skills): restore security-audit skill

* feat(skills): restore sentry skill

* feat(skills): restore shell-scripting skill

* feat(skills): restore slack-tools skill

* feat(skills): restore sql-analyst skill

* feat(skills): restore sqlite-expert skill

* feat(skills): restore sysadmin skill

* feat(skills): restore technical-writer skill

* feat(skills): restore terraform skill

* feat(skills): restore typescript-expert skill

* feat(skills): restore vector-db skill

* feat(skills): restore wasm-expert skill

* feat(skills): restore web-search skill

* feat(skills): restore writing-coach skill

skills/ml-engineer/SKILL.md

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+---
+name: ml-engineer
+description: "Machine learning engineer expert for PyTorch, scikit-learn, model evaluation, and MLOps"
+---
+# Machine Learning Engineer
+
+A machine learning practitioner with deep expertise in model development, training infrastructure, evaluation methodology, and production deployment. This skill provides guidance for building ML systems end-to-end using PyTorch for deep learning, scikit-learn for classical ML, and MLOps practices that ensure models are reproducible, monitored, and maintainable in production environments.
+
+## Key Principles
+
+- Start with a strong baseline using simple models and solid feature engineering before reaching for complex architectures; a well-tuned logistic regression often outperforms a poorly configured neural network
+- Evaluate models with metrics that align with business objectives, not just accuracy; precision, recall, F1, and AUC-ROC each tell different stories about model behavior on imbalanced data
+- Version everything: datasets, code, hyperparameters, and model artifacts; reproducibility is the foundation of trustworthy ML systems
+- Design training pipelines to be idempotent and resumable; checkpointing, deterministic seeding, and configuration files enable reliable experimentation
+- Monitor models in production for data drift, prediction drift, and performance degradation; a model that was accurate at deployment time can silently degrade as input distributions shift
+
+## Techniques
+
+- Structure PyTorch training with a clear pattern: define nn.Module subclass, configure DataLoader with proper num_workers and pin_memory, implement the training loop with optimizer.zero_grad(), loss.backward(), and optimizer.step()
+- Build scikit-learn pipelines with Pipeline and ColumnTransformer to chain preprocessing (scaling, encoding, imputation) with model fitting, ensuring that all transformations are fit on training data only
+- Perform hyperparameter tuning with GridSearchCV or RandomizedSearchCV using cross-validation; for expensive models, use Optuna or Bayesian optimization to search efficiently
+- Compute evaluation metrics on held-out test sets: classification_report for precision/recall/F1 per class, roc_auc_score for ranking quality, and confusion_matrix for error analysis
+- Engineer features systematically: log transforms for skewed distributions, interaction terms for feature combinations, target encoding for high-cardinality categoricals, and temporal features for time-series data
+- Track experiments with MLflow or Weights and Biases: log hyperparameters, metrics, artifacts, and model versions for every run
+
+## Common Patterns
+
+- **Train-Validate-Test Split**: Use stratified splitting (80/10/10) to maintain class distribution; never touch the test set during development, only for final evaluation
+- **Learning Rate Schedule**: Use warmup followed by cosine annealing or reduce-on-plateau for training stability; sudden large learning rates cause divergence in deep networks
+- **Ensemble Methods**: Combine predictions from diverse models (gradient boosting + neural network + linear model) to improve robustness and reduce variance
+- **Model Registry**: Promote models through stages (staging, production, archived) in MLflow Model Registry with approval gates and automated validation checks
+
+## Pitfalls to Avoid
+
+- Do not evaluate on the training set or leak test data into preprocessing; this produces overly optimistic metrics that do not reflect real-world performance
+- Do not train models without understanding the data: check for class imbalance, missing values, duplicates, and label noise before building any model
+- Do not deploy models without a rollback plan; maintain the previous model version in production so you can revert quickly if the new model underperforms
+- Do not treat feature engineering as a one-time task; as the domain evolves and new data sources become available, revisit and expand the feature set regularly