Add Dev Container and Claude Code skills

[MelbourneDeveloper]

TLDR;

Adds Dev Container for consistent development environment and Claude Code skills for multi-agent workflow.

What Does This Do?

This PR introduces a Dev Container configuration that pins Dart 3.10.7, Node 20.20.0, and includes pre-configured VSCode settings. It also adds 8 Claude Code skills to streamline common development tasks like testing, building, and creating PRs.

Brief Details?

• Dev Container: Added .devcontainer/ with Dockerfile, devcontainer.json, and post-create.sh that automatically installs all dependencies on container creation
• Claude Code Skills: Added 8 skills in .claude/skills/:
  • build-extension - Build and test VSCode extensions
  • create-pr - Create PRs using the dart_node template
  • pub-get - Install dependencies in dependency order
  • setup-claude - Install Claude Code CLI and Too Many Cooks extension
  • setup-playwright - Install Chromium and Playwright for E2E tests
  • taskflow - Build and run the full demo stack
  • test - Run tests and coverage with automatic package detection
  • website - Build and test the documentation site
• Scripts: Replaced run_dev.sh with examples/run_taskflow.sh for cleaner organization
• Dependencies: Upgraded npm packages (express 4.22.1, body-parser 1.20.4, qs 6.14.1, MCP SDK 1.25.3)
• Documentation: Updated CLAUDE.md, AGENTS.md, and READMEs with dev container info and PR guidelines

How Do The Tests Prove The Change Works?

The Dev Container has been tested by building the entire project via post-create.sh. The skills are invokable via /skill-name in Claude Code sessions. Dependency upgrades maintain backward compatibility (minor/patch versions only).