docs: add DataFusion security guidance

[efegokdemir]

Which issue does this PR close?

• Closes Add a "securing DataFusion" documentation #26061.

Rationale for this change

Applications embedding DataFusion may accept SQL from users, but the library guide does not explain security-relevant defaults or how available controls contribute to hardening.

What changes are included in this PR?

Adds a library guide covering SQL statement restrictions, opt-in local-file access, query memory limits, spill storage location and size limits, and the authorization and isolation responsibilities of the hosting application.

What is the testing strategy for this PR?

• ./ci/scripts/doc_prettier_check.sh (passed after the documentation update).

Are there any user-facing changes?

Adds a “Securing DataFusion” page to the Library User Guide and links it from the guide and documentation navigation. The page now explains that memory limits do not cap spill disk use and names the runtime settings for controlling temporary storage.

AI assistance was used in preparing this contribution.

[alamb]

@efegokdemir can you please confirm that you have reviewed the description and documentation of this PR?

The description seems like it may be unreviewed LLM output -- for example this line seems unrelated to this PR (and you can install it if you follow the README directions).

Sphinx HTML build not run: sphinx-build is not installed in this environment.

[alamb]

We are working on better AI policies

• Update contributor guidelines regarding AI spam, reviews, code #24510

[efegokdemir]

I reviewed the PR description and the new documentation page. I removed the unrelated Sphinx installation note from the testing section and retained only the documentation check that was run. AI assistance is disclosed in the PR description.

[samueleresca]

@efegokdemir The description of the PR not renders correctly after last update.

[alamb]

Thank you @efegokdemir -- this is looking close, I left some suggestions

[efegokdemir]

Updated in 8a146c79fc72ab4c7e693bb9888c68807c186375: the page now points to the project security policy, links DDL/DML examples and SessionContext::sql_with_options, uses the runtime settings guide for memory/spill controls, and removes repeated or vague guidance. ./ci/scripts/doc_prettier_check.sh --write --allow-dirty and git diff --check pass.

[alamb]

Looks good -- thank you @efegokdemir

[efegokdemir]

Fixed the Sphinx reference warning in 6be87571: the guide now links directly to the repository security policy instead of treating the root SECURITY.md as a Sphinx source document. ./ci/scripts/doc_prettier_check.sh --write --allow-dirty and git diff --check pass. A local full docs build was unavailable here (cargo-depgraph and the Sphinx Python module are not installed). The new Docs workflow is currently action_required with zero jobs, so there is no post-fix remote Sphinx result yet.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.74%. Comparing base (b40d696) to head (6be8757).
⚠️ Report is 49 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #26064      +/-   ##
==========================================
+ Coverage   82.69%   82.74%   +0.05%     
==========================================
  Files        1147     1147              
  Lines      447204   449767    +2563     
  Branches   447204   449767    +2563     
==========================================
+ Hits       369793   372154    +2361     
+ Misses      55001    54944      -57     
- Partials    22410    22669     +259     

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