feat(frontend): Update brand identity with new logo and color scheme.

- Add new Logo component with gradient design (blue #0b74de to cyan #06b6d4)
- Replace CreditCard icon with custom Logo in sidebar
- Update primary and secondary theme colors to match brand gradient
- Regenerate all PWA icons with new logo design
- Update theme colors in PWA manifest and meta tags
- Fix ESLint config to ignore generated PWA files

🤖 Generated with [Claude Code](https://claude.ai/code)

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

frontend/public/favicon.svg

@@ -1,4 +1,27 @@
-<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 32 32" fill="none">
-  <rect width="32" height="32" rx="6" fill="#3B82F6"/>
-  <path d="M8 24V8h6c2.2 0 4 1.8 4 4v4c0 2.2-1.8 4-4 4H12v4H8zm4-8h2c.6 0 1-.4 1-1v-2c0-.6-.4-1-1-1h-2v4z" fill="white"/>
+<svg xmlns="http://www.w3.org/2000/svg"
+     width="32" height="32"
+     viewBox="0 0 32 32"
+     role="img" aria-labelledby="title desc">
+  <title id="title">leggen — stylized italic L</title>
+  <desc id="desc">Square gradient background with italic white L.</desc>
+
+  <defs>
+    <linearGradient id="bg" x1="0" y1="0" x2="1" y2="1">
+      <stop offset="0%" stop-color="#0b74de"/>
+      <stop offset="100%" stop-color="#06b6d4"/>
+    </linearGradient>
+  </defs>
+
+  <!-- Square background -->
+  <rect width="32" height="32" fill="url(#bg)" rx="4"/>
+
+  <!-- Italic L -->
+  <text x="11" y="22"
+        font-family="Inter, Roboto, Arial, sans-serif"
+        font-weight="700"
+        font-size="20"
+        font-style="italic"
+        fill="#fff">
+    L
+  </text>
 </svg>