Feature request: Enable `Intent.EXTRA_ALLOW_MULTIPLE` for the Storage Access Framework (SAF) file picker

Currently, the intent used to invoke the system file picker (likely ACTION_OPEN_DOCUMENT or ACTION_GET_CONTENT) forces single-file selection. This creates a severe bottleneck for users who need to upload/add multiple files, as they have to trigger the intent repeatedly for each individual file.

Steps to Reproduce:

1. Launch the DashBeam app.
2. Trigger the action to add or upload a file, opening the Android system file picker.
3. Attempt to long-press a file to initiate multi-selection.
4. Expected result: The UI allows selecting additional files and confirming the batch.
5. Actual result: The picker instantly selects the single file, returns the URI to the app, and closes the picker.

Proposed Solution:

1. Append .putExtra(Intent.EXTRA_ALLOW_MULTIPLE, true) to the file picker intent payload.
2. Update the ActivityResultLauncher (or onActivityResult) implementation to parse intent.clipData (for multiple URIs) in addition to falling back on intent.data (for single URI selection).

Environment:

• Device: [Xiaomi 13T]
• OS: Android [16]
• App Version: [0.7.1]