WIP: Tailwind CSS v4 migration (incomplete)

[ericpgreen2]

Major changes in this migration attempt:

Package updates:

• Upgraded tailwindcss to v4.1.0
• Added @tailwindcss/vite plugin v4.1.0
• Removed autoprefixer (handled by v4)

Build configuration:

• Removed postcss.config.cjs from all packages (v4 handles internally)
• Updated vite configs to use @tailwindcss/vite plugin
• Switched from svelte-preprocess to vitePreprocess in svelte.config.js

Svelte components (187 files):

• Added @reference "tailwindcss" directive to all
• Required for @apply and theme() to work in component styles

CSS updates:

• Changed from @tailwind directives to @import "tailwindcss"
• Fixed custom utility classes that used @apply on other custom classes
• Created theme.css with @theme directive (incomplete)

Current blockers:

• Complex color system (506 CSS variables, dynamic light/dark switching)
• @theme definitions incomplete - colors not being recognized
• Need to decide on full migration strategy vs simplified color system

This commit saves progress for future reference. Build currently fails. Not ready for production.