DEVELOPMENT.md — contributor setup and architecture docs

[shanselman]

Summary

Add a DEVELOPMENT.md file documenting how to build, run, and contribute to the project.

Suggested Contents

Prerequisites

• .NET 9 SDK
• Windows 10/11 (WinUI3/WindowsAppSDK dependency)
• WebView2 Runtime (usually pre-installed on Windows 10+)
• A running Clawdbot gateway instance for testing

Project Structure

• Overview of the solution layout: Tray app, Shared library, PowerToys extension
• Which projects depend on what
• Where the gateway communication layer lives
• How the notification system works (event types, categories, routing)

Building

• dotnet build from solution root
• Any platform/architecture notes (arm64 vs x64)
• How to run in debug mode with Visual Studio or dotnet run

Architecture Overview

• Gateway SSE connection and reconnect/backoff logic
• Event parsing and structured notification types
• WebView2 lifecycle (WebChat panel, future Canvas panel)
• GDI handle management (icon creation/destruction pattern)
• Session tracking and polling
• Logging (file rotation, debug output)

Testing

• How to test without a live gateway
• Manual test scenarios for tray icon states, notifications, WebChat

CI

• GitHub Actions workflow overview
• What the CI build checks

Why This Matters

The repo is public and the project has a few moving parts (SSE streaming, WinUI3 tray, WebView2, PowerToys integration). Good contributor docs lower the barrier for PRs and help people understand the design decisions already made.

Acceptance Criteria

• DEVELOPMENT.md exists in repo root
• Covers build steps, prerequisites, and project structure
• Includes architecture overview with key design decisions
• Accurate and tested (someone can follow it cold and get a working build)