The Flatpak installs successfully on aarch64 (ARM64 / Asahi Linux), but fails immediately on execution.

The Flatpak installs successfully on `aarch64` (ARM64 / Asahi Linux), but fails immediately on execution. The wrapper script cannot locate the main executable.

### Steps to Reproduce
1. Install the Flatpak on an `aarch64` machine:
`flatpak install flathub net.code_industry.MasterPDFEditor`
2. Launch the application:
`flatpak run net.code_industry.MasterPDFEditor`

### Actual Behavior
The application fails to start and outputs the following error:
`/app/bin/masterpdfeditor5wrapper: line 4: /app/bin/masterpdfeditor5: No such file or directory`

### Additional Context & Root Cause
Inspecting the sandbox filesystem shows that `/app/bin/masterpdfeditor5` is a symlink pointing to `/app/extra/masterpdfeditor5`, but the `/app/extra` directory doesn't exist.

The `extra-data` download and extraction script in the manifest appears to be skipping or failing the file extraction process when executed on an `aarch64` host. Since the vendor now officially provides a native ARM64 Linux build (`master-pdf-editor-5.x.x-qt5.arm64.tar.gz`), the manifest needs to be updated to conditionally fetch the correct architecture package for `aarch64` refs.

Start by inspecting the Flatpak manifest's extra-data download and extraction logic, then check /app/bin/masterpdfeditor5wrapper and its /app/extra/masterpdfeditor5 target. Verify how the manifest handles aarch64 and the vendor's master-pdf-editor-5.x.x-qt5.arm64.tar.gz package. Done means the ARM64 package is extracted and the Flatpak launches successfully on aarch64.

Written by the indexing model from the issue text.