Consolidate DataFrame Docs: Merge HTML Rendering Section as Subpage

[kosiew]

Which issue does this PR close?

• Closes Merge dataframe documentation prior to release of DF48 #1158

Rationale for this change

Currently, the documentation includes redundant entries for "DataFrame" and "API", which causes confusion and reduces clarity. This change consolidates the DataFrame documentation, organizing the HTML rendering section as a dedicated subpage for better navigation and comprehension.

What changes are included in this PR?

• Merges duplicate dataframe.rst documents under a single structured user-guide/dataframe/index.rst
• Moves the HTML rendering guide into a new subpage: user-guide/dataframe/rendering.rst
• Updates all internal references to the relocated documentation paths
• Cleans up and simplifies the index.rst and api/index.rst to reflect the new structure

Are these changes tested?

These changes pertain to documentation structure. Manual validation was done via running the documentation generator to confirm the new structure renders correctly without broken links or formatting errors.

Are there any user-facing changes?

Yes. Users will now see a more streamlined documentation layout:

• A single, cohesive entry for "DataFrame" documentation
• A dedicated subpage for HTML rendering in Jupyter
• Improved navigation within the user guide via updated toctree structure

[timsaucer]

This is good, but I still see a couple of issues when I build it locally.

In the screen shot I am getting two different "API Reference" sections.

I think that if we move this section to the end of the entry point it will collapse down to one part. auto-api I believe is appending to the index at the end.

.. _toc.api:
.. toctree::
   :hidden:
   :maxdepth: 1
   :caption: API

   api/dataframe

But I think there is a more fundamental re-ordering we should do. Even if we move the snippet above to the bottom of the entry point we still have

1. "User Guide -> DataFrames" a page that has a very brief section about DataFrames and then a lot of information about formatting.
2. "User Guide -> DataFrames -> HTML Rendering in Jupyter" additional, and more detailed information about html rendering
3. "API -> DataFrame API" a page with some general usage patterns of DataFrames.

In terms of this numbered list, I think it would be easier to understand/follow if we

• Move the formatting information from (1) into (2)
• Move the content of (3) into (1) and delete file (3)

Then for the two pages, review to see if the flow of the information is clear. I suspect there would be some cleanup or deduplication we would want to do.

What do you think?

[kosiew]

Did you mean something like this?

[timsaucer]

I pushed a change to just move a few things over. We can open another PR if you feel strongly about splitting it out.