docs: realign docs to main and rewrite Fluid integration

[jlon]

Summary

• realign key documentation pages to the current main-branch implementation after pulling the latest curvine-doc structure changes
• rewrite the Fluid integration document from scratch based on the current curvine-docker/fluid code and manifests
• update CLI, UFS, cache, deploy, CSI, benchmark, development, and debugging docs to remove stale options, stale paths, and pre-release local references

Validation

• ran npm i in curvine-doc
• ran npm run build successfully for both en and zh-cn
• verified no unresolved merge markers remain
• verified no NFS / curvine-nfs / nfs-gateway references remain in the formal docs tree

Notes

• this PR intentionally avoids documenting unpublished local-branch-only content
• the remaining Docusaurus warnings are unrelated blog/tag hygiene warnings that pre-existed this doc update