docs(template): sync nanoclaw ca description

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Summary

• Sync the NanoClaw catalog XML with the normalized source template description format.

What changed

• Added the sectioned Community Apps overview copy for NanoClaw.
• Added the standard CA metadata stubs and Docker socket requirement copy.
• Kept repository, category, beta flag, appdata paths, and helper image identity unchanged.

Why

• The catalog copy should match the source repo template and render consistently with the rest of the AIO fleet in Community Apps.

Validation

• xmllint --noout nanoclaw-aio.xml
• aio-fleet validate-catalog --catalog-path <catalog-checkout>

Notes

• Catalog metadata only. No image, release, or runtime changes.