Extend copilot-instructions

[nirav-raval]

🎯 Aim

Improve copilot-instructions.md to give GitHub Copilot Agent clearer operational rules regarding branching, PR targets, dependency restrictions, and required use of contributing.md.

📷 Result

N/A

✅ What was done

• [X] Added rules enforcing dev branch as source and PR target
• [X] Added rule to always consult contributing.md
• [X] Added restriction preventing Copilot Agent from introducing new npm packages
• [X] Added restriction preventing updates to npm-shrinkwrap.json unless explicitly required
• [X] Updated context guidance for Copilot Agent

🔗 Related issue

Closes: #564

[Saurabh7019]

Thank you, @nirav-raval ! We will review it soon.

[Saurabh7019]

Hi @nirav-raval, could you please address the issues identified in the Copilot review before we test the flow? Also, 'Contribution & Branching Rules' section seems to be out of place. Could you add a new main section (right after 'Architecture Overview') called 'Key Considerations' and consolidate all of the do's and don'ts under it? including all your changes in - Contribution & Branching Rules, Extension Dependencies, File Changes & Documentation, Testing, and Security and privacy