feat: rebrand to Slate (logo, palette, copy, Launch button)

- Wordmark SVG + favicon (#FF1F8F → #00D4FF gradient)
- Page title: Slate — AI App Builder
- Header logo via inline component (no external font deps)
- Deploy button label -> Launch
- Chat placeholder + example prompt rebranded
- Replace upstream accent palette with magenta primary, add cyan2 for accents
- Settings tab notes upstream remains stackblitz-labs/bolt.diy

public/favicon.svg

@@ -1,4 +1,10 @@
-<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 16 16" width="16" height="16">
-  <rect width="16" height="16" rx="2" fill="#8A5FFF" />
-  <path d="M7.398 9.091h-3.58L10.364 2 8.602 6.909h3.58L5.636 14l1.762-4.909Z" fill="#fff" />
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 32 32" width="32" height="32">
+  <defs>
+    <linearGradient id="g" x1="0" y1="0" x2="1" y2="1">
+      <stop offset="0%" stop-color="#FF1F8F"/>
+      <stop offset="100%" stop-color="#00D4FF"/>
+    </linearGradient>
+  </defs>
+  <rect width="32" height="32" rx="7" fill="url(#g)"/>
+  <path d="M9.5 21.5c0 2.1 1.9 3.5 4.7 3.5 2.6 0 4.5-1.3 4.5-3.3 0-2-1.4-2.8-3.7-3.3l-1.7-.4c-2.7-.6-4.7-2-4.7-4.9 0-3.2 2.7-5.4 6.6-5.4 3.8 0 6.4 2 6.5 5.2h-3c-.1-1.7-1.5-2.7-3.5-2.7-2 0-3.4 1-3.4 2.5 0 1.5 1.2 2.3 3.4 2.7l1.7.4c3.1.7 5 2.2 5 5.1 0 3.6-2.7 5.8-7 5.8-4.1 0-6.9-2-7-5.4z" fill="#FFFFFF"/>
 </svg>