Fix GPX file opening, share sheet visibility, and add SAF track storage

Intent filter fixes:
- Remove pathSuffix=".gpx" + scheme restriction from the application/octet-stream
  ACTION_VIEW filter; pathSuffix matches the URI path, not the filename, so it
  never fired against file manager content URIs (opaque paths like /provider/uuid).
  The existing display-name check in handleIncomingGpx() is the correct gate.
- Add ACTION_SEND filter for application/octet-stream; Nav was invisible in share
  sheets because most file managers send this type for .gpx files.

SAF-based track storage (API 29+):
- Replace fragile SharedPrefs URI cache + OWNER_PACKAGE_NAME MediaStore query with
  Storage Access Framework as the primary write/read path. The user grants access to
  their tracks folder once via ACTION_OPEN_DOCUMENT_TREE; DocumentFile.listFiles()
  finds all GPX files without relying on MediaStore ownership (which Android clears
  on uninstall). After reinstall, a one-tap "Restore track access" button in Saved
  Tracks re-authorizes the same folder and all tracks immediately reappear.
- MediaStore path (existing) is kept as fallback for tracks saved before this change
- Add SafState enum (CONFIGURED / PERMISSION_LOST / NOT_CONFIGURED) in TrackStorage
- TrackRepository exposes safState() and initSafDirectory() thin wrappers
- MainViewModel exposes safState StateFlow and onSafDirectorySelected()
- SavedTracksFragment observes safState and shows contextual setup / re-auth button
- MainActivity registers safPickerLauncher and exposes launchSafPicker()
- Add androidx.documentfile:documentfile:1.0.1 dependency

https://claude.ai/code/session_01YUbuZNDAoLea4cf9UGQ9qn

1 files changed, 23 insertions, 6 deletions

diff --git a/android-app/app/src/main/res/layout/fragment_saved_tracks.xml b/android-app/app/src/main/res/layout/fragment_saved_tracks.xml
index 7485e59..a95b368 100644
--- a/android-app/app/src/main/res/layout/fragment_saved_tracks.xml
+++ b/android-app/app/src/main/res/layout/fragment_saved_tracks.xml
@@ -34,15 +34,32 @@
 
     </LinearLayout>
 
-    <TextView
-        android:id="@+id/tv_empty"
+    <LinearLayout
+        android:id="@+id/layout_empty"
         android:layout_width="match_parent"
         android:layout_height="match_parent"
+        android:orientation="vertical"
         android:gravity="center"
-        android:text="No saved tracks yet.\nRecord a trip to see it here."
-        android:textAlignment="center"
-        android:textColor="?attr/colorOnSurfaceVariant"
-        android:visibility="gone" />
+        android:padding="32dp"
+        android:visibility="gone">
+
+        <TextView
+            android:id="@+id/tv_empty"
+            android:layout_width="wrap_content"
+            android:layout_height="wrap_content"
+            android:text="No saved tracks yet.\nRecord a trip to see it here."
+            android:textAlignment="center"
+            android:textColor="?attr/colorOnSurfaceVariant" />
+
+        <com.google.android.material.button.MaterialButton
+            android:id="@+id/btn_setup_storage"
+            android:layout_width="wrap_content"
+            android:layout_height="wrap_content"
+            android:layout_marginTop="24dp"
+            android:text="Set up track storage"
+            android:visibility="gone" />
+
+    </LinearLayout>
 
     <androidx.recyclerview.widget.RecyclerView
         android:id="@+id/rv_saved_tracks"