feat: migrate downloads to public "Downloads/GitHub Store" directory

- Update `AndroidFileLocationsProvider` to use the public `DIRECTORY_DOWNLOADS` directory instead of app-private external storage.
- Modify `userDownloadsDir()` to return the same public path as `appDownloadsDir()`.
- Update `filepaths.xml` to include the new public path under `Download/GitHub Store/` for FileProvider access.
- Rename the existing private path to `ghs_legacy_downloads` in `filepaths.xml` to support migration from older versions.
- Ensure the "GitHub Store" subdirectory is created automatically within the public Downloads folder.

Author: rainxchzed

composeApp/src/androidMain/res/xml/filepaths.xml

@@ -1,8 +1,14 @@
 <?xml version="1.0" encoding="utf-8"?>
 <paths xmlns:android="http://schemas.android.com/apk/res/android">
 
-    <external-files-path
+    <!-- Public Downloads/GitHub Store folder (visible in file managers) -->
+    <external-path
         name="ghs_downloads"
+        path="Download/GitHub Store/" />
+
+    <!-- Legacy app-private downloads (for migration) -->
+    <external-files-path
+        name="ghs_legacy_downloads"
         path="/" />
 
     <cache-path

core/data/src/androidMain/kotlin/zed/rainxch/core/data/services/AndroidFileLocationsProvider.kt

@@ -1,20 +1,21 @@
 package zed.rainxch.core.data.services
 
 import android.content.Context
+import android.os.Environment
 import java.io.File
 
 class AndroidFileLocationsProvider(
     private val context: Context,
 ) : zed.rainxch.core.data.services.FileLocationsProvider {
     override fun appDownloadsDir(): String {
-        val externalFilesRoot = context.getExternalFilesDir(null)
-        val dir = File(externalFilesRoot, "ghs_downloads")
+        val publicDownloads = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS)
+        val dir = File(publicDownloads, "GitHub Store")
         if (!dir.exists()) dir.mkdirs()
         return dir.absolutePath
     }
 
     override fun userDownloadsDir(): String {
-        return "" // No-op
+        return appDownloadsDir()
     }
 
     override fun setExecutableIfNeeded(path: String) {