chore: Tailwind CSS v3 → v4 migration (#99)

* chore: run Tailwind v4 upgrade tool (Phase 1)

- Upgraded tailwindcss v3 → v4.2.1, postcss plugin to @tailwindcss/postcss
- Deleted tailwind.config.js, migrated theme to CSS @theme block in index.css
- Replaced @tailwind directives with @import 'tailwindcss'
- Added @custom-variant dark, @utility blocks for custom utilities
- Updated class names across 128 files (shadow-sm → shadow-xs, etc.)
- Removed autoprefixer (built into v4)
- Added migration plan doc

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* chore: switch from @tailwindcss/postcss to @tailwindcss/vite (Phase 2)

- Replaced @tailwindcss/postcss with @tailwindcss/vite plugin
- Deleted postcss.config.js (no longer needed)
- Tailwind now runs as a native Vite plugin for faster HMR

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* refactor: convert to OKLCH colors, move keyframes into @theme (Phase 3-4)

- Replaced all HSL color indirection with direct OKLCH values in @theme
- Moved all keyframes inside @theme block (v4 pattern)
- Eliminated hsl(var(--x)) double-indirection across 17 component files
- Replaced hsl() inline styles with var(--color-*) theme references
- Cleaned up redundant rdp-* utility blocks
- Fixed @custom-variant dark syntax to use :where()
- Added sidebar/glass/shadow vars as OKLCH in :root

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/components/library/ImportFlowModal.tsx

@@ -143,7 +143,7 @@ export function ImportFlowModal({ onClose }: ImportFlowModalProps) {
               />
               {parseError && (
                 <div className="flex items-start gap-2 rounded-lg border border-rose-500/20 bg-rose-500/5 px-3 py-2">
-                  <AlertTriangle className="mt-0.5 h-4 w-4 flex-shrink-0 text-rose-400" />
+                  <AlertTriangle className="mt-0.5 h-4 w-4 shrink-0 text-rose-400" />
                   <p className="text-xs text-rose-400">{parseError}</p>
                 </div>
               )}
@@ -165,7 +165,7 @@ export function ImportFlowModal({ onClose }: ImportFlowModalProps) {
                   maxLength={255}
                   className={cn(
                     'w-full rounded-lg border border-border bg-card px-3 py-2 text-sm text-foreground',
-                    'placeholder:text-muted-foreground focus:border-primary focus:outline-none focus:ring-1 focus:ring-primary/20'
+                    'placeholder:text-muted-foreground focus:border-primary focus:outline-hidden focus:ring-1 focus:ring-primary/20'
                   )}
                 />
               </div>