[Docs] Changelog doesn't call out breaking changes, no summary, fix/feat distinction muddled

### Describe the enhancement requested

It seems that the ~release notes~ changelog doesn't call out breaking changes at all - were there really none for v25.0.0? That'd be surprising given it's a major version.

See https://arrow.apache.org/release/25.0.0.html

In addition, the current distinction of commits into a) Fixes and b) Features seems muddled in practice.

Examples of things classified as features but sounds like fix/chore (semver minor)
- Avoid int64 overflow in CheckReadRangeOrThrow (#50060l)
- Enable auto GitHub Copilot review (#50630

~At least for major versions it would be nice to have a summary of the major changes (major features, breaking changes).~ this exists: Summary: https://arrow.apache.org/blog/2026/07/10/25.0.0-release/ but should be linked to from the changelog

### Component(s)

Documentation

Start by comparing the v25.0.0 changelog at https://arrow.apache.org/release/25.0.0.html with the linked release summary and inspect how changelog entries are generated and categorized. Done means the changelog clearly identifies breaking changes, distinguishes fixes from features, and links to the major-release summary.

Written by the indexing model from the issue text.