Add GitHub Copilot instructions for repository context

[Copilot]

Onboard repository to GitHub Copilot by providing AI context about project structure, conventions, and patterns.

Changes

• Created .github/copilot-instructions.md (210 lines)
  • Project architecture: Python 3.9+ visualization tool for dynamic programming on tree decompositions
  • Module purposes: visualization.py (core), reader.py (JSON/DIMACS parsing), svgjoin.py (SVG composition), construct_dpdb_visu.py (PostgreSQL integration)
  • Input/output specs: JSON API format, DIMACS tw/gr formats, SVG timestep outputs
  • Dev conventions: PEP 8, Google-style docstrings, pytest with hypothesis
  • Dependencies: Graphviz binary (>=2.38), graphviz Python package (>=0.20), psycopg[c], python-benedict[xml]
  • Platform-specific PostgreSQL client library installation guidance

Enables Copilot to generate context-aware suggestions aligned with project patterns and standards.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Onboard repository to GitHub Copilot</issue_title>
<issue_description>## Task
Onboard this repository to GitHub Copilot to leverage AI-powered code completion and suggestions for improved productivity.

Acceptance Criteria

• Enable GitHub Copilot for this repository.
• Verify that basic Copilot suggestions work for primary languages: Java, Python, Powershell, C++, Mathematica, and Neo4j/Cypher.
• Confirm team members have appropriate access.

Additional Notes

• See GitHub Copilot official docs for enablement instructions and best practices.
• Consider company or organizational policy requirements, if any, before enabling Copilot.
  </issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Onboard repository to GitHub Copilot #57

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.