Add E2B to the integrations catalog

[OndrejDrapalik]

Summary

• add E2B to the ADK integrations catalog
• document installation, a complete Agent, App, and runner example, the six sandbox tools, and configuration
• add the square E2B catalog icon and links to the published package and runnable examples

Verification

• clean-installed e2b-adk==0.1.0 from PyPI
• verified the example imports and constructs E2BPlugin, Agent, App, and InMemoryRunner with released google-adk==2.5.0
• verified all external links
• ran mkdocs build --strict against current google/adk-docs main
• confirmed the integration page, catalog card, and icon render

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