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/TreeTableView.tsx

@@ -173,13 +173,13 @@ export function TreeTableView({
                     {tree.name}
                   </span>
                   {tree.status === 'draft' && (
-                    <span className="inline-flex items-center gap-1 rounded-full bg-yellow-400/10 px-2 py-0.5 text-xs font-medium text-yellow-400 flex-shrink-0">
+                    <span className="inline-flex items-center gap-1 rounded-full bg-yellow-400/10 px-2 py-0.5 text-xs font-medium text-yellow-400 shrink-0">
                       <FileText className="h-3 w-3" />
                       Draft
                     </span>
                   )}
                   {tree.tree_type === 'maintenance' && (
-                    <span className="inline-flex items-center gap-1 rounded-full border border-amber-500/30 bg-amber-500/10 px-2 py-0.5 font-label text-[0.625rem] uppercase tracking-wide text-amber-400 flex-shrink-0">
+                    <span className="inline-flex items-center gap-1 rounded-full border border-amber-500/30 bg-amber-500/10 px-2 py-0.5 font-label text-[0.625rem] uppercase tracking-wide text-amber-400 shrink-0">
                       <Wrench className="h-3 w-3" />
                       Maintenance
                     </span>
@@ -191,11 +191,11 @@ export function TreeTableView({
                   )}
                   {tree.is_public ? (
                     <span title="Public tree">
-                      <Globe className="h-3.5 w-3.5 text-muted-foreground flex-shrink-0" />
+                      <Globe className="h-3.5 w-3.5 text-muted-foreground shrink-0" />
                     </span>
                   ) : (
                     <span title="Private tree">
-                      <Lock className="h-3.5 w-3.5 text-muted-foreground flex-shrink-0" />
+                      <Lock className="h-3.5 w-3.5 text-muted-foreground shrink-0" />
                     </span>
                   )}
                 </div>