Buckets docs

[Wauplin]

I think most of the content I can think of is already in the PR. Let me know if something's missing

Bucket page in PR docs: https://moon-ci-docs.huggingface.co/docs/hub/pr_2274/en/buckets

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Note

Low Risk
Documentation-only changes that add a new page and cross-links; low risk beyond potential broken links/anchors or nav rendering issues.

Overview
Introduces a new storage-buckets documentation page describing Storage Buckets (S3-like, mutable, non-versioned storage) with UI/CLI/Python workflows, file management (cp/sync/rm), CDN pre-warming, use cases, and pricing notes.

Surfaces this new doc throughout the Hub docs by adding it to _toctree.yml, adding a dedicated “Storage Buckets” card/links on index.md, and cross-linking from repositories.md plus updating storage-limits.md wording to explicitly include buckets.

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[HuggingFaceDocBuilderDev]

The docs for this PR live here. All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

[julien-c]

nice, let's go

(If possible @mishig25 @gary149 i would add a "NEW" tag somewhere in the doc to link to Storage Buckets to make sure it's highly visible)