feat: rename ClawChat → PinchChat across entire project

- Update package.json name and repo URL
- Update README.md, CONTRIBUTING.md branding and links
- Update UI components (Header, Chat) display names
- Update gateway user-agent string
- Rename GitHub repo via API
- Mark FEEDBACK.md item #1 as done

src/components/Chat.tsx

@@ -53,7 +53,7 @@ export function Chat({ messages, isGenerating, status, onSend, onAbort }: Props)
                   <Bot className="h-8 w-8 text-cyan-200" />
                 </div>
               </div>
-              <div className="text-lg text-zinc-200 font-semibold">ClawChat</div>
+              <div className="text-lg text-zinc-200 font-semibold">PinchChat</div>
               <div className="text-sm mt-1 text-zinc-500">Envoie un message pour commencer</div>
             </div>
           )}