fix: Add file extension to AppStream launchable field

[Fei1Yang]

When it means desktop-id, it actually means desktop-file.

Summary by Sourcery

Bug Fixes:

• Correct the AppStream launchable field by adding the file extension to the desktop-id.

[sourcery-ai]

Reviewer's Guide by Sourcery

This PR fixes the AppStream metadata by adding the .desktop file extension to the launchable field in the metainfo XML file. The change ensures proper desktop integration by correctly referencing the desktop entry file.

No diagrams generated as the changes look simple and do not need a visual representation.

File-Level Changes

Change	Details	Files
Update AppStream launchable field to include the .desktop extension	Change launchable desktop-id from 'rune' to 'rune.desktop' Fix compliance with AppStream specification for desktop entry references	assets/source/linux/rune.metainfo.xml

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[sourcery-ai]

Hey @Fei1Yang - I've reviewed your changes and they look great!

Here's what I looked at during the review

• 🟢 General issues: all looks good
• 🟢 Security: all looks good
• 🟢 Testing: all looks good
• 🟢 Complexity: all looks good
• 🟢 Documentation: all looks good

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