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/chat/BaseChat.tsx

@@ -563,7 +563,7 @@ export const BaseChat = React.forwardRef<HTMLDivElement, BaseChatProps>(
                         minHeight: TEXTAREA_MIN_HEIGHT,
                         maxHeight: TEXTAREA_MAX_HEIGHT,
                       }}
-                      placeholder="How can Bolt help you today?"
+                      placeholder="How can Slate help you today?"
                       translate="no"
                     />
                     <ClientOnly>