feat: migrate all icons to Lucide React

Replace unicode characters, emoji, and inline SVGs with lucide-react
components across the entire design system and page layer. Update
tests to assert on SVG elements instead of text content.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/pages/Inventory/sections/PrimitivesSection.tsx

@@ -1,4 +1,5 @@
 import { useState } from 'react'
+import { Search } from 'lucide-react'
 import styles from './PrimitivesSection.module.css'
 import {
   Alert,
@@ -358,7 +359,7 @@ export function PrimitivesSection() {
         description="Text input with optional leading icon and placeholder."
       >
         <Input placeholder="Plain input" />
-        <Input icon="🔍" placeholder="With icon" />
+        <Input icon={<Search size={14} />} placeholder="With icon" />
       </DemoCard>
 
       {/* 15b. InlineEdit */}