FRE-606: Add icon generation and tests for Tauri desktop

- Add generate-icons.sh script for cross-platform icon generation
- Generate all required icon sizes (32x32, 128x128, 256x256, 512x512)
- Create Windows .ico and macOS .icns icons
- Add Rust unit tests for core functionality
- Add tauri:test and tauri:icons npm scripts

New files:
- src-tauri/generate-icons.sh
- src-tauri/icons/32x32.png
- src-tauri/icons/128x128.png
- src-tauri/icons/128x128@2x.png
- src-tauri/icons/512x512.png
- src-tauri/icons/icon.ico
- src-tauri/icons/icon.icns
- src-tauri/icons/src/app-icon.svg
- src-tauri/icons/tray-icon.png
- src-tauri/src/tests.rs

Modified:
- src-tauri/src/lib.rs (added tests module)

src-tauri/icons/src/app-icon.svg

@@ -0,0 +1,21 @@
+<!-- FrenoCorp App Icon -->
+<!-- Base icon for generating all required sizes -->
+<svg width="1024" height="1024" viewBox="0 0 1024 1024" xmlns="http://www.w3.org/2000/svg">
+  <defs>
+    <linearGradient id="bgGradient" x1="0%" y1="0%" x2="100%" y2="100%">
+      <stop offset="0%" style="stop-color:#4A90D9;stop-opacity:1" />
+      <stop offset="100%" style="stop-color:#2E5C8A;stop-opacity:1" />
+    </linearGradient>
+  </defs>
+  
+  <!-- Background with rounded corners -->
+  <rect width="1024" height="1024" rx="180" ry="180" fill="url(#bgGradient)"/>
+  
+  <!-- Main F letter -->
+  <text x="512" y="720" font-family="Arial, sans-serif" font-size="600" font-weight="bold" fill="white" text-anchor="middle">
+    F
+  </text>
+  
+  <!-- Subtle highlight -->
+  <rect x="180" y="180" width="664" height="664" rx="120" ry="120" fill="none" stroke="rgba(255,255,255,0.2)" stroke-width="8"/>
+</svg>