Add in-app copy/move, background downloads, and a Favorites tab

- WebDAV MOVE/COPY-backed copy/move for files and folders, with a
  destination picker (independent nav state so it doesn't disturb the
  Files tab's browsing position) and a conflict-resolution sheet
  (overwrite all / keep both / decide per item).
- Downloads now use the same foreground-service + notification approach
  as uploads, surviving app closure.
- Favorites is now its own tab (account-wide, via a WebDAV SEARCH query)
  instead of a Files-tab filter toggle, which couldn't represent
  favorited items outside the currently browsed folder correctly.
- Share sheet restyled to match the app's design language, plus a
  "share file directly" action via the OS share sheet; details sheet
  tab icons resized to match the bottom nav.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

android/app/src/main/AndroidManifest.xml

@@ -2,12 +2,19 @@
     <uses-permission android:name="android.permission.INTERNET"/>
     <!-- For local_auth's biometric app-lock (Settings > Security). -->
     <uses-permission android:name="android.permission.USE_BIOMETRIC"/>
-    <!-- For ShareUploadService, which keeps a "Share to Noo" upload going
-         (and cancellable from its notification) even if the app is fully
-         closed - see the service's own doc comment. -->
+    <!-- For ShareUploadService/DownloadService, which keep a "Share to Noo"
+         upload/download going (and cancellable from its notification) even
+         if the app is fully closed - see each service's own doc comment. -->
     <uses-permission android:name="android.permission.FOREGROUND_SERVICE"/>
     <uses-permission android:name="android.permission.FOREGROUND_SERVICE_DATA_SYNC"/>
     <uses-permission android:name="android.permission.POST_NOTIFICATIONS"/>
+    <!-- DownloadService's pre-Android-10 fallback only (MediaStore.Downloads
+         needs no runtime permission on API 29+, which is what targetSdk
+         actually enforces) - capped with maxSdkVersion so it's not even
+         requested on newer devices. -->
+    <uses-permission
+        android:name="android.permission.WRITE_EXTERNAL_STORAGE"
+        android:maxSdkVersion="28"/>
     <application
         android:label="Noo"
         android:name="${applicationName}"
@@ -65,6 +72,10 @@
             android:name=".ShareUploadService"
             android:exported="false"
             android:foregroundServiceType="dataSync"/>
+        <service
+            android:name=".DownloadService"
+            android:exported="false"
+            android:foregroundServiceType="dataSync"/>
         <!-- Hands back the file(s) a caller picked via the GET_CONTENT filter
              above - only the app's own cache/picker/ subfolder is exposed,
              see file_paths.xml. -->