Normalize docs titles to sentence case

[Nabhye]

This PR standardizes documentation page titles and sidebar entries to use
sentence case, following the chosen documentation style.

Changes include:

• Updated topic page titles to sentence case
• Updated sidebar and topic index entries to match page titles
• Preserved anchors and filenames to avoid breaking links

This resolves the inconsistency between title- and sentence-cased headings
in the docs.

• Fixes Inconsistent title case in docs #3819

[Nabhye]

This PR only updates documentation title capitalization.
No functional or code changes were made.

[mhsmith]

Thanks, but there are several other places that will need to be updated in order to completely fix #3819. Most of these can be found in #4018 or its comments.

Also, the PR will need to include a change note. For instructions, please follow the "Check towncrier" link at the bottom of the PR page.

[HalfWhitt]

Thanks for adding the change note! Two things on that front:

• Change notes should be phrased the way you'd expect to see them in release notes, e.g., "Feature X has been added" rather than "Add feature X".
• The doc category is for actually substantial changes — things that would, in fact, warrant going in a version's release notes. For minor changes like this, misc is more appropriate.

Beyond that, as @mhsmith mentioned, there are more titles that are all capitalized, for example the three last pages under About Toga. And the tutorial titles, which are currently sentences / long phrases, need to be converted to simple, descriptive titles.

[Nabhye]

I’ve now updated the remaining About pages and converted tutorial titles to short, descriptive sentence-case titles, while avoiding sections likely to conflict. Please let me know if anything else should be adjusted.

[HalfWhitt]

Thanks for updating the change note, that looks great.

I’ve now updated the remaining About pages and converted tutorial titles to short, descriptive sentence-case titles

It doesn't look like that's in here... your commit named Normalize remaining About and tutorial titles to sentence case doesn't include any changes other than deleting the doc change note. Perhaps you forgot to stage your files when committing?

[HalfWhitt]

I'm not sure if you were planning to add more changes, but I notice that, similar to before, while your latest commit is named "Normalize remaining About and tutorial titles to sentence case", nothing's actually changed on the tutorials. (I see you have indeed fixed titles in About and Topics though, thank you.)

Once you're happy with how you have things and would like a re-review, feel free to leave a comment, or hit the refresh button next to where I'm listed as a reviewer.

[johnzhou721]

Also: The towncrier template in changes/ should also be normalized to sentence case, and we may want to edit past release notes as well.

[HalfWhitt]

Superseded by #4329.