Add ERC-4337 team logo to site header

- Move assets directory to docs/assets/ for MkDocs compatibility
- Configure Material theme to use ERC-4337-team-logo-white.png
- Add CSS styling for proper logo sizing (2rem height, max 200px width)
- Logo appears in top-left corner of site header
- All assets now properly served by MkDocs

Author: tomteman

docs/assets/images/ERC-4337-team-logo-color.png

@@ -37,3 +37,10 @@
 .md-typeset blockquote p {
     font-style: normal !important;
 }
+
+/* Logo styling */
+.md-header__button.md-logo img {
+    height: 2rem;
+    width: auto;
+    max-width: 200px;
+}

docs/assets/images/ERC-4337-team-logo-white.png

@@ -51,6 +51,7 @@ nav:
 
 theme:
   name: material
+  logo: assets/images/ERC-4337-team-logo-white.png
   features:
     - navigation.instant
     - navigation.top