refactor: split sidebar callout from generic Alert primitive

Rename CalloutCard to SidebarCallout (it was always sidebar-specific) and
add a shadcn-style Alert primitive with info/success/warning/error variants
for inline use in screens. Replace the misused SidebarCallout in project
settings with Alert and surface the underlying RPC error message instead
of generic copy. Tune destructive color per theme to a calm tinted red.

packages/app/src/components/left-sidebar.tsx

@@ -1,5 +1,5 @@
 import { router, usePathname } from "expo-router";
-import { MessagesSquare, Plus, Settings } from "lucide-react-native";
+import { FolderPlus, MessagesSquare, Settings } from "lucide-react-native";
 import {
   type Dispatch,
   memo,
@@ -365,7 +365,7 @@ function FooterIconButton({
   onPress: () => void;
   testID: string;
   accessibilityLabel: string;
-  icon: typeof Plus;
+  icon: typeof FolderPlus;
   theme: SidebarTheme;
 }) {
   return (
@@ -448,7 +448,7 @@ function SidebarFooter({
               onPress={handleOpenProject}
               testID="sidebar-add-project"
               accessibilityLabel="Add project"
-              icon={Plus}
+              icon={FolderPlus}
               theme={theme}
             />
           </TooltipTrigger>