Add prompt to make Stirling your default PDF app (#4890)

# Description of Changes
- Adds a reusable banner component/system to the core app
- Adds banner at the top of the desktop app if Stirling isn't your
default PDF editor, with a button to make it your default
- Adds a permanent button in the settings to do it manually (in case
you've dismissed the banner)
- Simplifies the file loading logic to fix a bug where the input file
could be duplicated occasionally. Now, the TS just receives files from
one buffer, regardless of how they've been passed to the app in Rust.

## Caveats
I've only been able to get the setting of default apps working properly
on Mac. The Windows build isn't signed (yet) so we can't use the proper
API for it, so currently it just sends you to the Settings UI. I've also
not been able to test it on Linux at all.

frontend/src/core/App.tsx

@@ -1,5 +1,6 @@
 import { Suspense } from "react";
 import { AppProviders } from "@app/components/AppProviders";
+import { AppLayout } from "@app/components/AppLayout";
 import { LoadingFallback } from "@app/components/shared/LoadingFallback";
 import HomePage from "@app/pages/HomePage";
 import OnboardingTour from "@app/components/onboarding/OnboardingTour";
@@ -16,8 +17,10 @@ export default function App() {
   return (
     <Suspense fallback={<LoadingFallback />}>
       <AppProviders>
-        <HomePage />
-        <OnboardingTour />
+        <AppLayout>
+          <HomePage />
+          <OnboardingTour />
+        </AppLayout>
       </AppProviders>
     </Suspense>
   );

frontend/src/core/components/AppLayout.tsx

@@ -0,0 +1,31 @@
+import { ReactNode } from 'react';
+import { useBanner } from '@app/contexts/BannerContext';
+
+interface AppLayoutProps {
+  children: ReactNode;
+}
+
+/**
+ * App layout wrapper that handles banner rendering and viewport sizing
+ * Automatically adjusts child components to fit remaining space after banner
+ */
+export function AppLayout({ children }: AppLayoutProps) {
+  const { banner } = useBanner();
+
+  return (
+    <>
+      <style>{`
+        .h-screen,
+        .right-rail {
+          height: 100% !important;
+        }
+      `}</style>
+      <div style={{ height: '100vh', display: 'flex', flexDirection: 'column' }}>
+        {banner}
+        <div style={{ flex: 1, minHeight: 0, height: 0 }}>
+          {children}
+        </div>
+      </div>
+    </>
+  );
+}

frontend/src/core/components/AppProviders.tsx

@@ -16,6 +16,7 @@ import { OnboardingProvider } from "@app/contexts/OnboardingContext";
 import { TourOrchestrationProvider } from "@app/contexts/TourOrchestrationContext";
 import { AdminTourOrchestrationProvider } from "@app/contexts/AdminTourOrchestrationContext";
 import { PageEditorProvider } from "@app/contexts/PageEditorContext";
+import { BannerProvider } from "@app/contexts/BannerContext";
 import ErrorBoundary from "@app/components/shared/ErrorBoundary";
 import { useScarfTracking } from "@app/hooks/useScarfTracking";
 import { useAppInitialization } from "@app/hooks/useAppInitialization";
@@ -50,22 +51,23 @@ export function AppProviders({ children, appConfigRetryOptions, appConfigProvide
     <PreferencesProvider>
       <RainbowThemeProvider>
         <ErrorBoundary>
-          <OnboardingProvider>
-            <AppConfigProvider
-              retryOptions={appConfigRetryOptions}
-              {...appConfigProviderProps}
-            >
-              <ScarfTrackingInitializer />
-              <FileContextProvider enableUrlSync={true} enablePersistence={true}>
-                <AppInitializer />
-                <ToolRegistryProvider>
-                  <NavigationProvider>
-                    <FilesModalProvider>
-                      <ToolWorkflowProvider>
-                        <HotkeyProvider>
-                          <SidebarProvider>
-                            <ViewerProvider>
-                              <PageEditorProvider>
+          <BannerProvider>
+            <OnboardingProvider>
+              <AppConfigProvider
+                retryOptions={appConfigRetryOptions}
+                {...appConfigProviderProps}
+              >
+                <ScarfTrackingInitializer />
+                <FileContextProvider enableUrlSync={true} enablePersistence={true}>
+                  <AppInitializer />
+                  <ToolRegistryProvider>
+                    <NavigationProvider>
+                      <FilesModalProvider>
+                        <ToolWorkflowProvider>
+                          <HotkeyProvider>
+                            <SidebarProvider>
+                              <ViewerProvider>
+                                <PageEditorProvider>
                                 <SignatureProvider>
                                   <RightRailProvider>
                                       <TourOrchestrationProvider>
@@ -76,16 +78,17 @@ export function AppProviders({ children, appConfigRetryOptions, appConfigProvide
                                   </RightRailProvider>
                                 </SignatureProvider>
                               </PageEditorProvider>
-                            </ViewerProvider>
-                          </SidebarProvider>
-                        </HotkeyProvider>
-                      </ToolWorkflowProvider>
-                    </FilesModalProvider>
-                  </NavigationProvider>
-                </ToolRegistryProvider>
-              </FileContextProvider>
-            </AppConfigProvider>
-          </OnboardingProvider>
+                              </ViewerProvider>
+                            </SidebarProvider>
+                          </HotkeyProvider>
+                        </ToolWorkflowProvider>
+                      </FilesModalProvider>
+                    </NavigationProvider>
+                  </ToolRegistryProvider>
+                </FileContextProvider>
+              </AppConfigProvider>
+            </OnboardingProvider>
+          </BannerProvider>
         </ErrorBoundary>
       </RainbowThemeProvider>
     </PreferencesProvider>

frontend/src/core/components/shared/InfoBanner.tsx

@@ -0,0 +1,72 @@
+import React from 'react';
+import { Paper, Group, Text, Button, ActionIcon } from '@mantine/core';
+import LocalIcon from '@app/components/shared/LocalIcon';
+
+interface InfoBannerProps {
+  icon: string;
+  message: string;
+  buttonText: string;
+  buttonIcon?: string;
+  onButtonClick: () => void;
+  onDismiss: () => void;
+  loading?: boolean;
+  show?: boolean;
+}
+
+/**
+ * Generic info banner component for displaying dismissible messages at the top of the app
+ */
+export const InfoBanner: React.FC<InfoBannerProps> = ({
+  icon,
+  message,
+  buttonText,
+  buttonIcon = 'check-circle-rounded',
+  onButtonClick,
+  onDismiss,
+  loading = false,
+  show = true,
+}) => {
+  if (!show) {
+    return null;
+  }
+
+  return (
+    <Paper
+      p="sm"
+      radius={0}
+      style={{
+        background: 'var(--mantine-color-blue-0)',
+        borderBottom: '1px solid var(--mantine-color-blue-2)',
+        position: 'relative',
+      }}
+    >
+      <Group gap="sm" align="center" wrap="nowrap">
+        <LocalIcon icon={icon} width="1.2rem" height="1.2rem" style={{ color: 'var(--mantine-color-blue-6)', flexShrink: 0 }} />
+        <Text fw={500} size="sm" style={{ color: 'var(--mantine-color-blue-9)' }}>
+          {message}
+        </Text>
+        <Button
+          variant="light"
+          color="blue"
+          size="xs"
+          onClick={onButtonClick}
+          loading={loading}
+          leftSection={<LocalIcon icon={buttonIcon} width="0.9rem" height="0.9rem" />}
+          style={{ flexShrink: 0 }}
+        >
+          {buttonText}
+        </Button>
+      </Group>
+      <ActionIcon
+        variant="subtle"
+        color="gray"
+        size="sm"
+        onClick={onDismiss}
+        aria-label="Dismiss"
+        style={{ position: 'absolute', top: '50%', right: '0.5rem', transform: 'translateY(-50%)' }}
+      >
+        <LocalIcon icon="close-rounded" width="1rem" height="1rem" />
+      </ActionIcon>
+    </Paper>
+  );
+};

frontend/src/core/contexts/BannerContext.tsx

@@ -0,0 +1,26 @@
+import { createContext, useContext, useState, ReactNode } from 'react';
+
+interface BannerContextType {
+  banner: ReactNode;
+  setBanner: (banner: ReactNode) => void;
+}
+
+const BannerContext = createContext<BannerContextType | undefined>(undefined);
+
+export function BannerProvider({ children }: { children: ReactNode }) {
+  const [banner, setBanner] = useState<ReactNode>(null);
+
+  return (
+    <BannerContext.Provider value={{ banner, setBanner }}>
+      {children}
+    </BannerContext.Provider>
+  );
+}
+
+export function useBanner() {
+  const context = useContext(BannerContext);
+  if (!context) {
+    throw new Error('useBanner must be used within BannerProvider');
+  }
+  return context;
+}