feat: redesign Manage tab to match reference layout

- Add Customization group: User Interface (CUI), Tool Palettes (large),
  Import, Export, Edit Aliases dropdown (small)
- Add Cleanup group: Find Non-Purgeable Items (large), Purge, Overkill, Audit (small)
- Add 8 new SVG icons for all new commands

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

assets/icons/find_nonpurgeable.svg

@@ -0,0 +1,8 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round">
+  <!-- Magnifier -->
+  <circle cx="10" cy="10" r="7"/>
+  <line x1="15" y1="15" x2="21" y2="21"/>
+  <!-- Lock inside (non-purgeable / protected) -->
+  <rect x="7" y="10" width="6" height="5" rx="0.5"/>
+  <path d="M8 10 V8 a2 2 0 0 1 4 0 V10"/>
+</svg>