Redesign the CakePHP 6 welcome page and application styles

[josbeir]

The welcome page and application layouts still depend on Milligram and bundled fonts. This replaces them with handwritten CSS and redesigns the CakePHP 6 welcome page without adding frontend dependencies, configuration, or a build step.

The welcome page shares resets, theme colors, typography, buttons, and accessibility styles with public/css/cake.css, while keeping its specific layout and animations inline. It introduces a responsive hero with the inline Cake logo, an animated gradient background and version number, grouped development checks, and a simpler footer with Discord. Reduced-motion and forced-colors preferences are supported.

Default and error layouts use the same stylesheet, including forms, tables, and Bake layouts. Flash messages gain keyboard-accessible dismiss buttons. Unused CSS and font assets are removed, and the README describes the new styling approach. Welcome-page tests cover successful and failed connections, escaped exception details, optional DebugKit, view blocks, and the production guard.

Dependency

This draft is stacked on #1109 and targets prepare/6.x-skeleton so the diff contains only the styling and welcome-page changes. Retarget to 6.x after that PR merges. PHP 8.5 requirements, CI, and attribute-resolver configuration comments remain in #1109.

Validation

• PHP 8.5.11: 21 tests / 65 assertions pass; PHP CodeSniffer, syntax checks, and git diff --check pass.
• Chromium: responsive layouts at 320–1440px, light/dark themes, hero alignment, keyboard skip link, reduced motion, forced colors, and asset loading checked. Firefox and Safari have not been tested.
• Composer dependencies were installed in an isolated temporary runtime using local CakePHP 6 and Migrations compatibility checkouts because of the upstream dependency blockers described in Prepare the application skeleton for CakePHP 6 #1109. No temporary repository overrides or preview fixtures are included in this PR.

Welcome/home dark and light

Application styles

Error pages