refactor: go fully native — remove all remaining shadcn component usage

Replace shadcn Select → native <select>:
- ascii/FontPreview.tsx: comment-style picker → glass pill wrapper
  with MessageSquareCode icon + native select
- color/ExportMenu.tsx: format + color-space pickers → native select
  with shared selectCls
- units/MainConverter.tsx: from/to unit pickers → native select

Delete dead code:
- components/media/FormatSelector.tsx (not imported anywhere,
  used shadcn Input + Label + Card)
- components/ui/select.tsx  — now unused
- components/ui/input.tsx   — now unused
- components/ui/label.tsx   — now unused
- components/ui/card.tsx    — now unused

Remaining components/ui/:
  slider.tsx, tooltip.tsx (TooltipProvider in Providers.tsx),
  slider-row.tsx, color-input.tsx

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

components/ascii/FontPreview.tsx

@@ -2,13 +2,6 @@
 
 import * as React from 'react';
 import { toPng } from 'html-to-image';
-import {
-  Select,
-  SelectContent,
-  SelectItem,
-  SelectTrigger,
-  SelectValue,
-} from '@/components/ui/select';
 import {
   Copy,
   Download,
@@ -205,19 +198,18 @@ export function FontPreview({
         </div>
 
         {/* Comment style */}
-        <Select value={commentStyle} onValueChange={(v) => setCommentStyle(v as CommentStyle)}>
-          <SelectTrigger className="h-7! w-auto gap-1.5 text-[10px] border-border/30 bg-transparent hover:border-primary/30 transition-colors">
-            <MessageSquareCode className="w-3 h-3 text-muted-foreground/60 shrink-0" />
-            <SelectValue />
-          </SelectTrigger>
-          <SelectContent>
+        <div className="flex items-center gap-1 px-2 py-1 glass rounded-md border border-border/30 text-muted-foreground hover:border-primary/30 hover:text-primary transition-colors">
+          <MessageSquareCode className="w-3 h-3 shrink-0" />
+          <select
+            value={commentStyle}
+            onChange={(e) => setCommentStyle(e.target.value as CommentStyle)}
+            className="bg-transparent outline-none text-[10px] font-mono cursor-pointer"
+          >
             {COMMENT_STYLES.map((s) => (
-              <SelectItem key={s.value} value={s.value}>
-                {s.label}
-              </SelectItem>
+              <option key={s.value} value={s.value}>{s.label}</option>
             ))}
-          </SelectContent>
-        </Select>
+          </select>
+        </div>
 
         {/* Stats */}
         {!isLoading && text && (