docs(readme): add Google ADK integration section

[shashi-stackone]

Summary

• Adds a collapsible Google ADK integration block to the Integration Examples
  section.
• Points users to the stackone-adk plugin, which is the first-party ADK
  integration listed at https://adk.dev/integrations/stackone/ and compatible with
  ADK 2.0.
• Code matches the canonical example published on the ADK documentation site.

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Summary by cubic

Adds a collapsible Google ADK integration example to the README, showing how to use StackOne with ADK 2.0 via the stackone-adk plugin. Includes a runnable snippet and an install command.

• New Features
  • Collapsible section with an ADK 2.0 example using stackone-adk.
  • Adds uv add stackone-adk and a link to the plugin docs for configuration and search_and_execute mode.

^{Written for commit 534eccf. Summary will update on new commits.}

[Copilot]

Pull request overview

This PR expands the README’s “Integration Examples” by adding a new collapsible section documenting how to integrate StackOne with Google’s Agent Development Kit (ADK) via the stackone-adk plugin.

Changes:

• Adds a “Google ADK Integration” <details> block under Integration Examples.
• Provides installation and a minimal async example using StackOnePlugin with an ADK Agent/App and InMemoryRunner.
• Links to the stackone-adk integration page and the plugin repository for configuration details.

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[cubic-dev-ai]

No issues found across 1 file

_{Auto-approved: This change only adds a documentation section to the README with a code example and installation instructions, with no modifications to source code, configuration, or critical systems.}

[willleeney]

lgtm