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/src/components/ui/logo.tsx

@@ -0,0 +1,44 @@
+interface LogoProps {
+  className?: string;
+  size?: number;
+}
+
+export function Logo({ className = "", size = 32 }: LogoProps) {
+  return (
+    <svg
+      xmlns="http://www.w3.org/2000/svg"
+      width={size}
+      height={size}
+      viewBox="0 0 32 32"
+      className={className}
+      role="img"
+      aria-labelledby="logo-title logo-desc"
+    >
+      <title id="logo-title">leggen — stylized italic L</title>
+      <desc id="logo-desc">Square gradient background with italic white L.</desc>
+
+      <defs>
+        <linearGradient id="logo-bg" x1="0" y1="0" x2="1" y2="1">
+          <stop offset="0%" stopColor="#0b74de" />
+          <stop offset="100%" stopColor="#06b6d4" />
+        </linearGradient>
+      </defs>
+
+      {/* Square background */}
+      <rect width="32" height="32" fill="url(#logo-bg)" rx="4" />
+
+      {/* Italic L */}
+      <text
+        x="11"
+        y="22"
+        fontFamily="Inter, Roboto, Arial, sans-serif"
+        fontWeight="700"
+        fontSize="20"
+        fontStyle="italic"
+        fill="#fff"
+      >
+        L
+      </text>
+    </svg>
+  );
+}