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

app/components/@settings/tabs/update/UpdateTab.tsx

@@ -455,7 +455,7 @@ const UpdateTab = () => {
             <div className="flex items-center justify-between">
               <div>
                 <p>
-                  Updates are fetched from: <span className="font-mono">stackblitz-labs/bolt.diy</span> (
+                  Updates are fetched from: <span className="font-mono">stackblitz-labs/bolt.diy</span> (Slate upstream) (
                   {isLatestBranch ? 'main' : 'stable'} branch)
                 </p>
                 <p className="mt-1">
@@ -553,7 +553,7 @@ const UpdateTab = () => {
           <DialogDescription>
             <div className="mt-4">
               <p className="text-sm text-bolt-elements-textSecondary mb-4">
-                A new version is available from <span className="font-mono">stackblitz-labs/bolt.diy</span> (
+                A new version is available from <span className="font-mono">stackblitz-labs/bolt.diy</span> (Slate upstream) (
                 {isLatestBranch ? 'main' : 'stable'} branch)
               </p>