Add comprehensive .github/copilot-instructions.md for efficient AI agent onboarding

[Copilot]

This PR adds a comprehensive .github/copilot-instructions.md file to significantly improve the efficiency of AI coding agents working with the plodo repository. The instructions provide essential information that reduces exploration time and prevents common build failures.

What's included

Repository Overview & Architecture

• Complete description of the 3-component system (API, Client Web App, Presenter Desktop App)
• Technology stack details (.NET 8.0, Vue.js 2.x, Electron, Cassandra)
• High-level project structure and architectural patterns

Validated Build Instructions
All build procedures have been tested and documented with specific workarounds:

# API Backend - Works correctly
cd api/
dotnet build plodo.Backend.API/plodo.Backend.API.csproj

# Client Web App - Requires Node.js compatibility workaround
cd client-app/
NODE_OPTIONS="--openssl-legacy-provider" npm run build

# Presenter App - Platform restrictions documented
cd presenter-app/
# Fails on Linux - Windows/macOS only

Critical Workarounds Documented

• Legacy Project Exclusion: Must avoid plodo.Backend.API.old (incompatible .NET Core 3.1)
• Node.js Compatibility: Requires NODE_OPTIONS="--openssl-legacy-provider" for Vue.js builds
• Package Manager Issues: Use npm instead of yarn to avoid dependency conflicts
• Platform Restrictions: Presenter app cannot be built on Linux

Project Layout & Configuration

• Detailed directory structure with file purposes
• Key configuration files and their roles (appsettings.json, vue.config.js, etc.)
• Hidden dependencies and environment variables
• Azure DevOps CI/CD pipeline information

Validation Steps
Pre-tested commands for agents to verify their changes don't break existing functionality, including specific files to avoid modifying.

Impact

This documentation will help AI agents:

• ✅ Reduce build failures by providing tested commands and known workarounds
• ✅ Minimize exploration time with comprehensive project layout information
• ✅ Avoid breaking changes through validation steps and file modification guidelines
• ✅ Work more efficiently with ready-to-use build procedures

The instructions follow the 2-page limit requirement and focus on practical, actionable information rather than task-specific guidance.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• https://storage.googleapis.com/chromium-browser-snapshots/Linux_x64/686378/chrome-linux.zip
  • Triggering command: /usr/local/bin/node install.js (http block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

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💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.