Introduce Google ADK TypeScript as a skill

[fahmidme]

Summary

This PR introduces a new curated skill: Google ADK TypeScript (adk-js).

It adds a comprehensive SKILL.md along with focused reference documentation that covers the full ADK JS workflow end-to-end, including:

• Project scaffolding and quickstart for TypeScript
• Model and authentication setup (Gemini API key vs Vertex AI)
• ADK devtools (CLI and web UI)
• LLM agent configuration (schemas, outputKey, context handling)
• Tooling patterns (FunctionTool, built-ins like GOOGLE_SEARCH, AgentTool)
• Multi-agent orchestration (orchestrator + sequential, parallel, and loop agents)
• Callbacks, guardrails, and human-in-the-loop patterns
• Practical Next.js integration notes
• Common failure modes and debugging guidance

Motivation

The goal is to make it easy to scaffold, run, and evolve ADK agents in TypeScript using official, docs-backed patterns while avoiding common pitfalls. The references are modular and opinionated toward production-ready usage rather than one-off demos.

Scope

• Adds a new curated skill under skills/.curated/google-adk-js
• Includes architecture guidance, tooling docs, model/auth notes, and real-world integration considerations
• No breaking changes or modifications to existing skills

Notes

This skill is designed to be used when users ask to build or extend ADK agents in TypeScript, design multi-agent workflows, add tools, or adapt patterns directly from the ADK JS documentation and samples.