docs: update v2026.4.306 changelog with detailed release notes}
- Replace placeholder changelog entries with comprehensive release notes
- Document ReJSON (JSON data type) support features: view, create, edit,
format, copy, and download JSON documents
- Document auto-detection of Redis modules via MODULE LIST
- Document JSON keys tree icon and Add Key dialog support
- Document Electron webview to iframe migration refactor
- Document OnPush change detection and markForCheck refactors
- Document bugfixes for Electron loading spinner, search filter restore,
and Add Key dialog prefix
- Document i18n additions for 21 languages and README updates
- Document removal of armv7l (32-bit ARM) build targets