Configure comprehensive Copilot instructions for repository best practices (#923)

.github/copilot-instructions.md

@@ -1,5 +1,19 @@
 # GitHub Copilot Agent Instructions for MQTT Explorer
 
+## Overview
+
+MQTT Explorer is an Electron-based desktop application for exploring MQTT brokers. It provides a comprehensive UI for connecting to MQTT brokers, browsing topics, and analyzing message flows.
+
+## Technology Stack
+
+- **Frontend**: React 16.x with Material-UI
+- **Backend**: Node.js with TypeScript
+- **Desktop Framework**: Electron 29.x
+- **MQTT Client**: [mqttjs](https://github.com/mqttjs/MQTT.js) v4.x
+- **State Management**: Redux with redux-thunk
+- **Build Tools**: webpack, TypeScript compiler
+- **Testing**: Mocha + Chai for unit tests, Playwright for MCP introspection tests
+
 ## Project Setup
 
 ### Building and Running
@@ -97,9 +111,128 @@ The project supports MCP (Model Context Protocol) for automated testing with Pla
 - `src/` - Electron main process and bindings
 - `src/spec/` - Test specifications including MCP introspection tests
 
+## Code Style and Formatting
+
+### Linting
+
+The project uses TSLint with Airbnb config and Prettier for code formatting:
+
+```bash
+# Run all linters
+yarn lint
+
+# Run linters individually
+yarn lint:prettier    # Check Prettier formatting
+yarn lint:tslint      # Check TSLint rules
+yarn lint:spellcheck  # Check spelling in code
+
+# Auto-fix issues
+yarn lint:fix         # Fix TSLint and Prettier issues
+yarn lint:tslint:fix  # Fix TSLint issues only
+yarn lint:prettier:fix # Fix Prettier issues only
+```
+
+### Code Style Rules
+
+- **Semicolons**: Never use semicolons (enforced by TSLint and Prettier)
+- **Quotes**: Single quotes for strings
+- **Indentation**: 2 spaces
+- **Line length**: Maximum 120 characters (Prettier) / 200 characters (TSLint)
+- **Arrow functions**: No parentheses for single parameters (`x => x + 1`)
+- **Trailing commas**: Required for multiline objects and arrays (ES5 compatible)
+
+### TypeScript Guidelines
+
+- Enable strict null checks and no implicit any
+- Use TypeScript interfaces for data structures
+- Prefer `const` over `let`, avoid `var`
+- Use type inference when possible, explicit types when clarity is needed
+
+## Dependency Management
+
+### Adding Dependencies
+
+```bash
+# Add to root project
+yarn add <package-name>
+
+# Add to app (frontend)
+cd app && yarn add <package-name>
+
+# Add to backend
+cd backend && yarn add <package-name>
+
+# Add dev dependencies
+yarn add -D <package-name>
+```
+
+### Important Dependency Notes
+
+- Main dependencies are in the root `package.json`
+- Frontend React app has its own dependencies in `app/package.json`
+- Backend models and logic have dependencies in `backend/package.json`
+- Always use `--frozen-lockfile` in CI to ensure reproducible builds
+- Run `yarn install` after pulling changes that modify `yarn.lock`
+
+## Debugging
+
+### Development Mode
+
+```bash
+# Start with hot reload for frontend
+yarn dev
+
+# This runs two processes in parallel:
+# 1. webpack-dev-server for the React app (port varies)
+# 2. Electron in development mode with the --development flag
+```
+
+### Debugging TypeScript
+
+- Source maps are enabled in `tsconfig.json`
+- Use `ts-node` for running TypeScript files directly
+- Backend tests can be debugged with: `cd backend && yarn test-inspect`
+
+### Common Issues
+
+- **Build fails**: Clear `dist/` and `app/build/` directories, then rebuild
+- **Electron won't start**: Ensure `yarn build` completed successfully
+- **Tests fail**: Check if MQTT broker (mosquitto) is running for integration tests
+- **UI not updating**: In dev mode, ensure webpack-dev-server is running
+
+## Deployment and Packaging
+
+### Creating Releases
+
+```bash
+# Prepare release (updates version, changelog)
+yarn prepare-release
+
+# Package the application for distribution
+yarn package
+
+# Package with Docker (for consistent builds)
+yarn package-with-docker
+```
+
+### Release Workflow
+
+- **Beta releases**: Create PR to `beta` branch with "feat:" or "fix:" commits
+- **Production releases**: Create PR to `release` branch with "feat:" or "fix:" commits
+- Semantic release automatically handles versioning and changelog
+- Builds are created for Windows, macOS, and Linux
+
+### Build Artifacts
+
+- Output directory: `build/`
+- Supported formats: DMG (macOS), EXE/NSIS (Windows), AppImage/Snap (Linux), AppX (Windows Store)
+- Code signing is configured via `res/` directory certificates and provisioning profiles
+
 ## Important Notes
 
 - Always run `yarn build` before starting the application
 - The app uses Electron (see `package.json` for version)
 - MQTT communication is handled via [mqttjs](https://github.com/mqttjs/MQTT.js)
 - All code changes should pass linting (`yarn lint`)
+- Node.js version requirement: >= 18
+- The project uses workspace-like structure with separate package.json files for app and backend