perf(ui): migrate icons to SVG sprite system

Replace @remixicon/react with a shared Icon component that renders
via <use href> references to a single hidden SVG sprite. This reduces
DOM node count by replacing inline SVGs with lightweight references.

- Create Icon component with sprite injection (packages/ui/src/components/icon/)
- Migrate all 164 files from @remixicon/react to Icon component
- Auto-generate sprite data from remixicon bundle (scripts/generate-icon-sprite.mjs)
- Add bun run icons:generate to package.json
- Move @remixicon/react to devDependencies
- Add icon usage instructions to theme-system skill

packages/ui/src/components/views/git/WorktreeBranchDisplay.tsx

@@ -1,6 +1,6 @@
 import React from 'react';
-import { RiGitBranchLine, RiEditLine, RiCheckLine, RiCloseLine, RiLoader4Line } from '@remixicon/react';
 import { Button } from '@/components/ui/button';
+import { Icon } from "@/components/icon/Icon";
 import { useI18n } from '@/lib/i18n';
 
 interface WorktreeBranchDisplayProps {
@@ -86,7 +86,7 @@ export const WorktreeBranchDisplay: React.FC<WorktreeBranchDisplayProps> = ({
             handleSaveEdit();
           }}
         >
-          <RiGitBranchLine className="size-4 text-primary" />
+          <Icon name="git-branch" className="size-4 text-primary" />
           <input
             ref={inputRef}
             value={editBranchName}
@@ -104,9 +104,9 @@ export const WorktreeBranchDisplay: React.FC<WorktreeBranchDisplayProps> = ({
             className="shrink-0 text-muted-foreground hover:text-foreground disabled:opacity-50"
           >
             {isRenaming ? (
-              <RiLoader4Line className="size-4 animate-spin" />
+              <Icon name="loader-4" className="size-4 animate-spin" />
             ) : (
-              <RiCheckLine className="size-4" />
+              <Icon name="check" className="size-4" />
             )}
           </button>
           <button
@@ -117,7 +117,7 @@ export const WorktreeBranchDisplay: React.FC<WorktreeBranchDisplayProps> = ({
             title={t('gitView.branch.renameCancel')}
             className="shrink-0 text-muted-foreground hover:text-foreground disabled:opacity-50"
           >
-            <RiCloseLine className="size-4" />
+            <Icon name="close" className="size-4" />
           </button>
         </form>
       </div>
@@ -126,7 +126,7 @@ export const WorktreeBranchDisplay: React.FC<WorktreeBranchDisplayProps> = ({
 
   return (
     <div className="flex w-full min-w-0 items-center gap-1.5 px-2 py-1 h-8">
-      <RiGitBranchLine className="size-4 text-primary shrink-0" />
+      <Icon name="git-branch" className="size-4 text-primary shrink-0" />
       <div className="inline-flex min-w-0 max-w-full items-center gap-1">
         <span className="truncate typography-ui-label font-normal text-foreground">
           {currentBranch || t('gitView.branch.detachedHead')}
@@ -139,7 +139,7 @@ export const WorktreeBranchDisplay: React.FC<WorktreeBranchDisplayProps> = ({
             onClick={handleStartEdit}
             title={t('gitView.branch.renameTitle')}
           >
-            <RiEditLine className="size-4" />
+            <Icon name="edit" className="size-4" />
           </Button>
         )}
       </div>