Add theme showcase pages, Playwright screenshot tests, and Tailwind theme

[Copilot]

Captures screenshots of all UI themes via Playwright and adds a Tailwind CSS theme. Improves the Bootstrap theme based on visual review.

Theme Showcase

New /theme-showcase/{theme} routes rendering all core components (Buttons, Cards, Form Controls, Tags, Progress, Table, Bar) under each theme. Shared ThemeShowcase.svelte component, per-theme route pages for default, bootstrap, tailwind, dark.

Playwright Screenshot Tests

• playwright.config.ts + tests/theme-screenshots.spec.ts capturing full-page screenshots of each theme
• npm run test:screenshots to regenerate screenshots/ directory
• .gitignore updated for test-results/, playwright-report/

New Tailwind Theme

src/lib/vars/themes/tailwind.css — Tailwind default design tokens: blue-500 primary, gray palette, ui-sans-serif stack, rounded-md borders, cubic-bezier(0.4, 0, 0.2, 1) transitions, tamed checkbox affordances. Registered in Themes.svelte switcher.

Bootstrap Theme Improvements

• --warning-text-transform: none — Bootstrap doesn't uppercase warning buttons
• Added --container-bg, --card-header-bg, --card-footer-bg for proper card chrome
• Added --shadow-color, --link-fg, --progress-bar-color, --progress-track-bg
• Updated --code-font-family to Bootstrap's SFMono stack
• Tamed checkbox hover/active affordances

Bootstrap

Tailwind

Dark

Default

Note: Svelte devDependency bumped to v4 to resolve pre-existing incompatibility with @sveltejs/kit@2.5.17 (the v3 dep couldn't start the dev server). peerDependencies already allowed ^3.0.0 || ^4.0.0.

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