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>
           )}

src/components/Header.tsx

@@ -23,7 +23,7 @@ export function Header({ status, sessionKey, onToggleSidebar, activeSessionData
         </div>
         <div className="min-w-0">
           <div className="flex items-center gap-2">
-            <span className="font-semibold text-zinc-300 text-sm tracking-wide">ClawChat</span>
+            <span className="font-semibold text-zinc-300 text-sm tracking-wide">PinchChat</span>
             <Sparkles className="h-3.5 w-3.5 text-cyan-300/60" />
           </div>
           <span className="text-xs text-zinc-500 truncate block">{sessionLabel}</span>