Add three specialist neural routing papers

[uu231]

Summary

Adds structured research notes for three specialist constructive neural routing solvers:

• An Efficient Graph Convolutional Network Technique for the Travelling Salesman Problem
• Combinatorial Optimization by Graph Pointer Networks and Hierarchical Reinforcement Learning
• Efficiently Solving the Practical Vehicle Routing Problem: A Novel Joint Learning Approach

The notes summarize each paper's motivation, contributions, methodology, experiments, limitations, and reproducibility information.

Checklist

• Paper id matches its filename.
• Scope and paradigm follow the repository definitions.
• Front Matter includes every required field.
• The note includes all required research sections.
• Claims are neutral and traceable to original sources.
• Generated README index blocks and src/generated/ were not edited manually.
• npm run validate, npm test, and npm run build pass locally, when Node.js is available.