Android: `file_picker` rejects `gguf` and `task`` custom extensions with `Unsupported filter` exception

[ASahu16]

Attempting to open the file picker with custom extensions gguf and task on Android fails with a PlatformException. The Android logs indicate that both extensions are considered unsupported and ignored.
Logs:

W/FilePickerUtils(18387): Custom file type gguf is unsupported and will be ignored.
W/FilePickerUtils(18387): Custom file type task is unsupported and will be ignored.
D/FilePickerUtils(18387): Allowed file extensions mimes: []
I/flutter (18387): [MethodChannelFilePicker] Platform exception: PlatformException(FilePicker, Unsupported filter. Make sure that you are only using the extension without the dot, (ie., jpg instead of .jpg). This could also have happened because you are using an unsupported file extension.  If the problem persists, you may want to consider using FileType.any instead., null, null)
I/flutter (18387): 2026-07-09T10:42:08.300037 [ERROR] Zone: Uncaught zone error
I/flutter (18387): error: PlatformException(FilePicker, Unsupported filter. Make sure that you are only using the extension without the dot, (ie., jpg instead of .jpg). This could also have happened because you are using an unsupported file extension.  If the problem persists, you may want to consider using FileType.any instead., null, null)
I/flutter (18387): #0      StandardMethodCodec.decodeEnvelope (package:flutter/src/services/message_codecs.dart:653:7)
message_codecs.dart:653
I/flutter (18387): #1      MethodChannel._invokeMethod (package:flutter/src/services/platform_channel.dart:366:18)
platform_channel.dart:366
I/flutter (18387): <asynchronous suspension>
I/flutter (18387): #2      MethodChannel.invokeListMethod (package:flutter/src/services/platform_channel.dart:552:35)
platform_channel.dart:552
I/flutter (18387): <asynchronous suspension>
I/flutter (18387): #3      FilePickerIO._getPath (package:file_picker/src/file_picker_io.dart:103:33)
file_picker_io.dart:103
I/flutter (18387): <asynchronous suspension>
I/flutter (18387): #4      ModelsNotifier.sideloadModel (package:loki_llm/features/models/presentation/models_notifier.dart:115:20)
models_notifier.dart:115
I/flutter (18387): <asynchronous suspension>
I/flutter (18387): 

[ASahu16]

Triaged for v1.2.0. Still open — ModelsNotifier.sideloadModel uses FileType.custom with gguf/task; Android rejects unsupported MIME filters. Likely fix: FileType.any + client-side extension validation.