Compatible with PHP 8.1 to 8.5

• Fix PWA theme color (#5757)
• Add security check to prevent access to sensitive data in twig export templates (#5757)
• Re-introduced computed fallback color for all API entities color-safe which will never be null (#5757)
• Fix calendar colors (#5757)

Involved in this release: @kevinpapst, @HUSEYNKHANLI