Rename and update notebook 306_4: pedagogical focus on outlier rejection with isolation forests

- Rename notebook from Anomaly_detection to Outlier_rejection_isolation_forests
- Add definitions of outliers, anomalies, and novelties
- Add citations to Liu et al. 2008 (Isolation Forest), Malanchev et al. 2021 (ZTF)
- Add context about ZTF anomaly detection pipelines
- Mention other techniques (OCSVM, autoencoders, LOF) with citations
- Retarget notebook as pedagogical tool for understanding ML with different dimensions
- Limit data to bright but not-too-bright stars (r_scienceFluxMean 1e4-5e5 nJy)
- Expand exercises section with feature exploration tasks
- Reference tutorials 207.1 and 207.2 for feature descriptions
- Follow RTN-045 guidelines for notebook structure

Author: plazas