Fix Polycentric profile file import in MainActivity

- Update handleUnknownText method to detect Polycentric profile data
- Check for 'polycentric://' prefix in shared text files
- Launch PolycentricImportProfileActivity when Polycentric profile is detected
- Add logging for Polycentric profile detection
- Fixes 'unknown url format' error when sharing Polycentric profile files to Grayjay

This completes the file sharing workflow: users can now export Polycentric
profiles to files and share them to Grayjay, which will automatically
detect and import the profile data.

app/src/main/java/com/futo/platformplayer/activities/MainActivity.kt

@@ -994,6 +994,15 @@ class MainActivity : AppCompatActivity, IWithResultLauncher {
 
     fun handleUnknownText(text: String): Boolean {
         try {
+            // Check for Polycentric profile data
+            if (text.startsWith("polycentric://")) {
+                Logger.i(TAG, "Detected Polycentric profile in shared text file")
+                startActivity(Intent(this, PolycentricImportProfileActivity::class.java).apply { 
+                    putExtra("url", text.trim()) 
+                })
+                return true;
+            }
+            
             if (text.startsWith("@/Subscription") || text.startsWith("Subscriptions")) {
                 val lines = text.split("\n").map { it.trim() }.drop(1).filter { it.isNotEmpty() };
                 navigate(_fragImportSubscriptions, lines);