feat: restructure repo for collaboration + add desktop app source

- Reorganize project: clean structure (portable/ u-claw-app/ usb-scripts/ website/)
- Move docs into website/, rename uclaw-scripts to usb-scripts
- Add u-claw-app/ Electron desktop source code
- Add portable/setup.sh: one-command dev environment setup
- Add portable/SkillHub.html: skill marketplace page
- Update README: dev guide, contribution workflow, project structure
- Update .gitignore: exclude runtime binaries and build artifacts
- Expand China install guide: npm mirrors, detailed onboard wizard

u-claw-app/assets/icon.svg

@@ -0,0 +1,54 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 1024 1024">
+  <defs>
+    <linearGradient id="bg" x1="0%" y1="0%" x2="100%" y2="100%">
+      <stop offset="0%" style="stop-color:#1a1a2e"/>
+      <stop offset="100%" style="stop-color:#0a0a1a"/>
+    </linearGradient>
+    <linearGradient id="claw" x1="0%" y1="0%" x2="100%" y2="100%">
+      <stop offset="0%" style="stop-color:#ff8f65"/>
+      <stop offset="100%" style="stop-color:#ff6b35"/>
+    </linearGradient>
+    <filter id="glow">
+      <feGaussianBlur stdDeviation="8" result="blur"/>
+      <feMerge><feMergeNode in="blur"/><feMergeNode in="SourceGraphic"/></feMerge>
+    </filter>
+  </defs>
+
+  <!-- Background -->
+  <rect width="1024" height="1024" rx="200" fill="url(#bg)"/>
+
+  <!-- Outer ring -->
+  <circle cx="512" cy="512" r="420" fill="none" stroke="#ff6b35" stroke-width="6" opacity="0.15"/>
+  <circle cx="512" cy="512" r="380" fill="none" stroke="#ff6b35" stroke-width="3" opacity="0.1"/>
+
+  <!-- Lobster/Claw body -->
+  <g filter="url(#glow)">
+    <!-- Main claw shape -->
+    <path d="M280 440 C280 280, 400 180, 512 300 C624 180, 744 280, 744 440 C744 600, 660 720, 512 760 C364 720, 280 600, 280 440Z"
+          fill="url(#claw)" opacity="0.95"/>
+
+    <!-- Left pincer -->
+    <path d="M320 380 C280 300, 220 320, 240 380 C260 440, 310 420, 340 400Z"
+          fill="#ff8f65" opacity="0.8"/>
+
+    <!-- Right pincer -->
+    <path d="M704 380 C744 300, 804 320, 784 380 C764 440, 714 420, 684 400Z"
+          fill="#ff8f65" opacity="0.8"/>
+  </g>
+
+  <!-- U letter -->
+  <path d="M380 400 L380 560 C380 640, 440 700, 512 700 C584 700, 644 640, 644 560 L644 400"
+        fill="none" stroke="#ffffff" stroke-width="40" stroke-linecap="round" stroke-linejoin="round"/>
+
+  <!-- Eyes -->
+  <circle cx="430" cy="360" r="24" fill="#ffffff"/>
+  <circle cx="594" cy="360" r="24" fill="#ffffff"/>
+  <circle cx="435" cy="355" r="10" fill="#1a1a2e"/>
+  <circle cx="599" cy="355" r="10" fill="#1a1a2e"/>
+
+  <!-- Antennae -->
+  <path d="M430 320 C420 260, 360 220, 320 200" fill="none" stroke="#ff8f65" stroke-width="8" stroke-linecap="round" opacity="0.7"/>
+  <path d="M594 320 C604 260, 664 220, 704 200" fill="none" stroke="#ff8f65" stroke-width="8" stroke-linecap="round" opacity="0.7"/>
+  <circle cx="316" cy="196" r="12" fill="#ff6b35" opacity="0.8"/>
+  <circle cx="708" cy="196" r="12" fill="#ff6b35" opacity="0.8"/>
+</svg>