Change backup file names

We use the application ID now to ensure uniqueness if the same folder is selected
between different app versions/forks. This will make more sense once storage
settings are unified to a single location.

Also changes the file extension while we're at it so people stop accidentally
ungzipping it.

app/src/main/java/eu/kanade/tachiyomi/data/backup/models/Backup.kt

@@ -1,5 +1,6 @@
 package eu.kanade.tachiyomi.data.backup.models
 
+import eu.kanade.tachiyomi.BuildConfig
 import kotlinx.serialization.Serializable
 import kotlinx.serialization.protobuf.ProtoNumber
 import java.text.SimpleDateFormat
@@ -16,11 +17,11 @@ data class Backup(
 ) {
 
     companion object {
-        val filenameRegex = """tachiyomi_\d+-\d+-\d+_\d+-\d+.proto.gz""".toRegex()
+        val filenameRegex = """${BuildConfig.APPLICATION_ID}_\d+-\d+-\d+_\d+-\d+.tachibk""".toRegex()
 
         fun getFilename(): String {
             val date = SimpleDateFormat("yyyy-MM-dd_HH-mm", Locale.getDefault()).format(Date())
-            return "tachiyomi_$date.proto.gz"
+            return "${BuildConfig.APPLICATION_ID}_$date.tachibk"
         }
     }
 }