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/desktop/hooks/useOpenedFile.ts

@@ -1,45 +1,46 @@
 import { useState, useEffect } from 'react';
 import { fileOpenService } from '@app/services/fileOpenService';
+import { listen } from '@tauri-apps/api/event';
 
 export function useOpenedFile() {
   const [openedFilePaths, setOpenedFilePaths] = useState<string[]>([]);
   const [loading, setLoading] = useState(true);
 
   useEffect(() => {
-    const checkForOpenedFile = async () => {
-      console.log('🔍 Checking for opened file(s)...');
+    // Function to read and process files from storage
+    const readFilesFromStorage = async () => {
+      console.log('🔍 Reading files from storage...');
       try {
         const filePaths = await fileOpenService.getOpenedFiles();
         console.log('🔍 fileOpenService.getOpenedFiles() returned:', filePaths);
 
         if (filePaths.length > 0) {
-          console.log(`✅ App opened with ${filePaths.length} file(s):`, filePaths);
+          console.log(`✅ Found ${filePaths.length} file(s) in storage:`, filePaths);
           setOpenedFilePaths(filePaths);
-
-          // Clear the files from service state after consuming them
           await fileOpenService.clearOpenedFiles();
-        } else {
-          console.log('ℹ️ No files were opened with the app');
         }
-
       } catch (error) {
-        console.error('❌ Failed to check for opened files:', error);
+        console.error('❌ Failed to read files from storage:', error);
       } finally {
         setLoading(false);
       }
     };
 
-    checkForOpenedFile();
+    // Read files on mount
+    readFilesFromStorage();
 
-    // Listen for runtime file open events (abstracted through service)
-    const unlistenRuntimeEvents = fileOpenService.onFileOpened((filePath: string) => {
-      console.log('📂 Runtime file open event:', filePath);
-      setOpenedFilePaths(prev => [...prev, filePath]);
+    // Listen for files-changed events (when new files are added to storage)
+    let unlisten: (() => void) | undefined;
+    listen('files-changed', async () => {
+      console.log('📂 files-changed event received, re-reading storage...');
+      await readFilesFromStorage();
+    }).then(unlistenFn => {
+      unlisten = unlistenFn;
     });
 
     // Cleanup function
     return () => {
-      unlistenRuntimeEvents();
+      if (unlisten) unlisten();
     };
   }, []);