feat: GitOps workflow for WebSearch ADK Agent

[ypeng1]

Summary

This PR adds CI validation for the WebSearch ADK agent and updates the WebSearch template for LangChain 0.3.x compatibility.

Changes

1. Reusable GitHub Action for ADK Agent Validation

• New action: .github/actions/run-adk-agent
  • Runs gradient agent run to validate that an ADK agent starts and is reachable at http://localhost:8080
  • Supports configurable working-directory, python-version, and API keys
  • Uses DIGITALOCEAN_INFERENCE_KEY for LLM calls; optional OPENAI_API_KEY for RAG embeddings
• Workflow: .github/workflows/validate-websearch.yml
  • Runs on PRs that touch WebSearch/** and on workflow_dispatch
  • Uses the new action to validate the WebSearch agent

2. Composite Action Fix

• Added required shell: bash to run steps in the composite action for correct execution.

3. LangChain 0.3.x Compatibility (WebSearch)

• Dependencies (WebSearch/requirements.txt): Pinned to LangChain 0.3.x for compatibility with langchain-gradient.
• Agent implementation (WebSearch/main.py): Switched to langgraph.prebuilt.create_react_agent for LangChain 0.3.x support.

Testing

• WebSearch agent validated via the new GitHub Action workflow.
• Requires DIGITALOCEAN_INFERENCE_KEY in repo secrets for CI to pass.