Overhaul releases docs, add branches page

[huntie]

Note

Stacked PR: Depends on #5186, #5187, #5188.

Summary

A new, stronger home for Releases information on reactnative.dev.

1. The versioning/release pages had become somewhat hidden under Docs > Guides and an expandable side nav section. The refreshed Releases Overview page now presents essential info in a single view, accessible from a top-level Releases nav item.

   

2. For framework/library maintainers, we've had no central source for what each release branch contains. The new Branches page introduces an initial table of platform components by branch, inspired by Chromium Dash.

   

3. Revise all content. Generally, the Releases Overview page retains everything a first-timer would need to understand. Cut out/relocate passive information such as number of intended releases/philosophy.

   • The Versioning Policy core guidance is untouched.

Deliberate choices

• Separated from the docs — in future, potentially a dynamic section of the site (out of scope today).
• The Release Levels page (user guidance on Canary etc. feature level opt-in) remains, for now, under Docs (relocated to Docs > Guides > Workflow).

Other changes

• Add _redirects entries mapping the old /docs/releases/* URLs to the new locations, and fix two stale versioning-policy redirects.
• Table styling: Both release tables get a shaded, bold row-header column and single-line cells that scroll horizontally within their bordered wrapper.

Test Plan

Screen.Recording.2026-07-25.at.18.11.49.mov

• ✅ Tour of new Releases pages
• ✅ Docs version switcher navigates to /versions within our new hierachy
• Switch to 0.85 docs (old versions) (left hand side)
  • ✅ Releases section in Docs sidebar (previous state, unchanged)
  • ✅ All pages present (previous state, unchanged)