chore: Add rebrand assets, implementation guide, and gitignore local settings

Adds brand-assets/ (SVGs, brand guide) and REBRAND-IMPLEMENTATION-GUIDE.md
as reference docs. Removes .claude/settings.local.json from tracking
(contains local permissions and tokens).

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

brand-assets/favicon.svg

@@ -0,0 +1,18 @@
+<svg viewBox="0 0 32 32" fill="none" xmlns="http://www.w3.org/2000/svg">
+  <defs>
+    <linearGradient id="fav-gradient" x1="0%" y1="0%" x2="100%" y2="0%">
+      <stop offset="0%" stop-color="#818cf8"/>
+      <stop offset="100%" stop-color="#a78bfa"/>
+    </linearGradient>
+  </defs>
+  
+  <!-- Simplified icon for small sizes -->
+  <!-- Input circles -->
+  <circle cx="5" cy="8" r="2.5" fill="url(#fav-gradient)" opacity="0.35"/>
+  <circle cx="5" cy="16" r="3" fill="url(#fav-gradient)" opacity="0.5"/>
+  <circle cx="5" cy="24" r="2.5" fill="url(#fav-gradient)" opacity="0.35"/>
+  <!-- Center node -->
+  <circle cx="14" cy="16" r="4" fill="url(#fav-gradient)"/>
+  <!-- Arrow -->
+  <path d="M18 16H28M28 16L24 12M28 16L24 20" stroke="url(#fav-gradient)" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"/>
+</svg>