Add Keenable integration

[ilya-bogin-keenable]

Adds the Keenable integration to the catalog.

Keenable is a web search and page-fetch API built for AI agents. The keenable-haystack package provides two Haystack 2.x components:

• KeenableWebSearch — returns documents + links (the same output shape as SerperDevWebSearch / SearchApiWebSearch, so it drops into existing web-search pipelines).
• KeenableFetcher — fetches URLs and returns their main content as markdown Documents (extracted server-side, so no separate LinkContentFetcher + HTMLToDocument step).

Keyless by default (public endpoints, no signup); an optional KEENABLE_API_KEY lifts rate limits.

• PyPI: https://pypi.org/project/keenable-haystack
• Repo: https://github.com/keenableai/keenable-haystack

Adds integrations/keenable.md and logos/keenable.png (400×400).

[vercel]

@ilya-bogin-keenable is attempting to deploy a commit to the deepset Team on Vercel.

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