Add CONTRIBUTING.md to outline development setup and contribution process

CONTRIBUTING.md

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+# Contributing to Llamactl
+
+Thank you for considering contributing to Llamactl! This document outlines the development setup and contribution process.
+
+## Development Setup
+
+### Prerequisites
+
+- Go 1.24 or later
+- Node.js 22 or later
+- `llama-server` executable (from [llama.cpp](https://github.com/ggml-org/llama.cpp))
+
+### Getting Started
+
+1. **Clone the repository**
+   ```bash
+   git clone https://github.com/lordmathis/llamactl.git
+   cd llamactl
+   ```
+
+2. **Install dependencies**
+   ```bash
+   # Go dependencies
+   go mod download
+   
+   # Frontend dependencies
+   cd webui && npm ci && cd ..
+   ```
+
+3. **Run for development**
+   ```bash
+   # Start backend server
+   go run ./cmd/server
+   ```
+   Server will be available at `http://localhost:8080`
+   
+   ```bash
+   # In a separate terminal, start frontend dev server
+   cd webui && npm run dev
+   ```
+   Development UI will be available at `http://localhost:5173`
+
+4. **Common development commands**
+   ```bash
+   # Backend
+   go test ./... -v                    # Run tests
+   go test -race ./... -v              # Run with race detector
+   go fmt ./... && go vet ./...        # Format and vet code
+   
+   # Frontend (run from webui/ directory)
+   npm run test:run                    # Run tests once
+   npm run test                        # Run tests in watch mode
+   npm run type-check                  # TypeScript type checking
+   npm run lint:fix                    # Lint and fix issues
+   ```
+
+## Before Submitting a Pull Request
+
+### Required Checks
+
+All the following must pass:
+
+1. **Backend**
+   ```bash
+   go test ./... -v
+   go test -race ./... -v
+   go fmt ./... && go vet ./...
+   go build -o llamactl ./cmd/server
+   ```
+
+2. **Frontend**
+   ```bash
+   cd webui
+   npm run test:run
+   npm run type-check
+   npm run build
+   ```
+
+### API Documentation
+
+If changes affect API endpoints, update Swagger documentation:
+
+```bash
+# Install swag if needed
+go install github.com/swaggo/swag/cmd/swag@latest
+
+# Update Swagger comments in pkg/server/handlers.go
+# Then regenerate docs
+swag init -g cmd/server/main.go -o apidocs
+```
+
+## Pull Request Guidelines
+
+### Pull Request Titles
+Use this format for pull request titles:
+- `feat:` for new features
+- `fix:` for bug fixes  
+- `docs:` for documentation changes
+- `test:` for test additions or modifications
+- `refactor:` for code refactoring
+
+### Submission Process
+1. Create a feature branch from `main`
+2. Make changes following the coding standards
+3. Run all required checks listed above
+4. Update documentation if necessary
+5. Submit pull request with:
+   - Clear description of changes
+   - Reference to any related issues
+   - Screenshots for UI changes
+
+## Code Style and Testing
+
+### Testing Strategy
+- Backend tests use Go's built-in testing framework
+- Frontend tests use Vitest and React Testing Library
+- Run tests frequently during development
+- Add tests for new features and bug fixes
+
+### Go
+- Follow standard Go formatting (`go fmt`)
+- Use meaningful variable and function names  
+- Add comments for exported functions and types
+- Handle errors appropriately
+
+### TypeScript/React
+- Use TypeScript strictly (avoid `any` when possible)
+- Follow React hooks best practices
+- Use meaningful component and variable names
+- Prefer functional components over class components
+
+## Getting Help
+
+- Check existing [issues](https://github.com/lordmathis/llamactl/issues)
+- Review the [README.md](README.md) for usage documentation  
+- Look at existing code for patterns and conventions
+
+Thank you for contributing to Llamactl!