feat (change-history): add sidebar with topbar toggle

[tunjiadeyemi]

Description

This PR adds an API Change History feature to Swagger UI so users can quickly see what changed between OpenAPI spec reloads.

Implemented:

• New change-history core plugin with Redux state/actions/selectors
• Local snapshot persistence in localStorage (keyed by spec URL)
• Spec diff engine for:
  • endpoint add/remove/modify
  • parameter/request/response changes
  • schema add/remove and property-level schema diffs
  • tags/info/security changes
  • media-type changes
• History UI moved to a right sidebar
• History trigger moved to top bar as a history icon (next to dark mode toggle), with unseen-change badge
• Light/dark mode styling for the sidebar and controls

Motivation and Context

When backend teams update the OpenAPI document, frontend/API consumers currently have no native way in Swagger UI to track what changed. They must manually compare specs.
This feature adds built-in change visibility by capturing snapshots and presenting a readable history timeline of changes after reloads.
Fixes #10951

How Has This Been Tested?

• Manual testing:

  • Ran local dev server and loaded specs from local/dev sources
  • Verified baseline snapshot is created on first load
  • Reloaded modified specs and verified history entries update correctly
  • Verified history icon badge appears for unseen changes
  • Verified sidebar open/close behavior (button, backdrop, close button)
  • Verified light/dark mode color behavior for sidebar controls

• Automated testing:

  • Ran targeted unit tests for change-history:
  • test/unit/core/plugins/change-history/fn.test.js
  • test/unit/core/plugins/change-history/container.jsx
  • test/unit/core/plugins/change-history/sidebar.jsx
  • test/unit/standalone/plugins/top-bar/ChangeHistoryToggle.jsx
    Result: all relevant tests passed

Screenshots (if appropriate):

Checklist

My PR contains...

• No code changes (src/ is unmodified: changes to documentation, CI, metadata, etc.)
• Dependency changes (any modification to dependencies in package.json)
• Bug fixes (non-breaking change which fixes an issue)
• Improvements (misc. changes to existing features)
• Features (non-breaking change which adds functionality)

My changes...

• are breaking changes to a public API (config options, System API, major UI change, etc).
• are breaking changes to a private API (Redux, component props, utility functions, etc.).
• are breaking changes to a developer API (npm script behavior changes, new dev system dependencies, etc).
• are not breaking changes.

Documentation

• My changes do not require a change to the project documentation.
• My changes require a change to the project documentation.
• If yes to above: I have updated the documentation accordingly.

Automated tests

• My changes can not or do not need to be tested.
• My changes can and should be tested by unit and/or integration tests.
• If yes to above: I have added tests to cover my changes.
• If yes to above: I have taken care to cover edge cases in my tests.
• All new and existing tests passed.