feat: add search functionality to templates and extensions pages

[ulises-jeremias]

Describe the feature

Client-side search/filter for templates and extensions catalog pages.

Use Case

Hard to find a slug when the catalog grows (AI/ML addons).

Proposed Solution

Filter by name/slug/labels; reuse patterns from Create-Node-App website if present.

Other Information

Maintainer-seeded Hacktoberfest issue.

Acknowledgements

• I may be able to implement this feature request
• This feature might incur a breaking change

Version used

website @ main

Environment details (OS name and version, etc.)

n/a (docs/site contribution)