feat: wire up HTTP definition headers orthogonally from auth, remove uninstall confirm

- Headers from server definitions are now always applied as default_headers
  on the reqwest::Client regardless of auth strategy (OAuth, PAT, or no-auth)
- If headers contain an Authorization header, OAuth is skipped entirely
- If headers have no Authorization, they ride alongside OAuth tokens
- Add build_default_headers() and build_http_client() helpers
- Remove standalone connect_with_headers() in favor of orthogonal design
- Add 19 unit tests for HttpTransport (requires_oauth, header building,
  connect routing logic, transport_type, description)
- Remove broken confirm() dialog from server uninstall action

Signed-off-by: Mohammod Al Amin Ashik <maa.ashik00@gmail.com>

Author: its-mash

apps/desktop/src/features/servers/ServersPage.tsx

@@ -709,15 +709,9 @@ export function ServersPage() {
   };
 
   const handleUninstall = async (server: ServerViewModel) => {
-    // Import source-aware helpers
-    const { getUninstallConfirmMessage, getUninstallLabel } = await import('@/components/SourceBadge');
-    const confirmMsg = getUninstallConfirmMessage(server.name, server.installation_source);
+    const { getUninstallLabel } = await import('@/components/SourceBadge');
     const actionLabel = getUninstallLabel(server.installation_source);
-    
-    if (!confirm(confirmMsg)) {
-      return;
-    }
-    
+
     setActionLoading(`uninstall-${server.id}`);
     try {
       const { uninstallServer } = await import('@/lib/api/registry');