Add logo icon to components and update branding assets

- Integrated `logo-icon.svg` into headers, footer, and development layout for consistent branding.
- Updated `logo.svg` and `logo-icon.svg` with improved gradient and filter naming for clarity.
- Enhanced `README.md` and branding documentation with logo visuals and descriptions.
- Refined visual identity details in docs to emphasize the branding hierarchy and usage.

frontend/src/app/icon.svg

@@ -0,0 +1,11 @@
+<svg width="32" height="32" viewBox="0 0 32 32" fill="none" xmlns="http://www.w3.org/2000/svg">
+  <defs>
+    <linearGradient id="grad1" x1="0%" y1="0%" x2="100%" y2="100%">
+      <stop offset="0%" style="stop-color:#0EA5E9;stop-opacity:1" />
+      <stop offset="100%" style="stop-color:#2563EB;stop-opacity:1" />
+    </linearGradient>
+  </defs>
+  <path d="M16 26L4 20L16 14L28 20L16 26Z" fill="url(#grad1)" opacity="0.6" />
+  <path d="M16 21L4 15L16 9L28 15L16 21Z" fill="url(#grad1)" opacity="0.8" />
+  <path d="M16 16L4 10L16 4L28 10L16 16Z" fill="url(#grad1)" />
+</svg>