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/desktop/updates/update-callout-source.tsx

@@ -1,8 +1,11 @@
 import { Gift } from "lucide-react-native";
 import { type ReactNode, useEffect, useRef } from "react";
 import { useUnistyles } from "react-native-unistyles";
-import { CalloutDescriptionText } from "@/components/callout-card";
-import { type SidebarCalloutAction, useSidebarCallouts } from "@/contexts/sidebar-callout-context";
+import {
+  type SidebarCalloutAction,
+  SidebarCalloutDescriptionText,
+} from "@/components/sidebar-callout";
+import { useSidebarCallouts } from "@/contexts/sidebar-callout-context";
 import { useDesktopAppUpdater } from "@/desktop/updates/use-desktop-app-updater";
 import { useStableEvent } from "@/hooks/use-stable-event";
 import { openExternalUrl } from "@/utils/open-external-url";
@@ -167,14 +170,14 @@ export function UpdateCalloutSource() {
 function UpdateAvailableDescription({ versionLabel }: { versionLabel?: string }) {
   return (
     <>
-      <CalloutDescriptionText>
+      <SidebarCalloutDescriptionText>
         {versionLabel
           ? `${versionLabel} is ready to install.`
           : "A new version is ready to install."}
-      </CalloutDescriptionText>
-      <CalloutDescriptionText>
+      </SidebarCalloutDescriptionText>
+      <SidebarCalloutDescriptionText>
         Upgrading the app will stop running agents and close terminal sessions.
-      </CalloutDescriptionText>
+      </SidebarCalloutDescriptionText>
     </>
   );
 }