ci(github): implement proper AppImage generation for Linux

[rainxchzed]

This commit replaces the simple tar.gz packaging of the application binaries with a proper .AppImage build process using appimagetool. It configures the necessary AppDir structure, including the AppRun entry point, desktop integration, and icon assets.

• ci(github): Integrated appimagetool into the build-desktop-platforms workflow for the Linux "modern" matrix.
• ci(github): Implemented AppDir creation logic with custom AppRun script and .desktop file generation.
• ci(github): Updated the upload artifact step to provide the .AppImage file directly instead of a compressed archive.
• chore: Disabled artifact compression for the AppImage as the format is already compressed.

Summary by CodeRabbit

• Chores
  • Improved AppImage build and packaging process for Linux platform distributions.

[coderabbitai]

Caution

Review failed

The pull request is closed.

ℹ️ Recent review info

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between fb501f9 and eb73817.

📒 Files selected for processing (1)

• .github/workflows/build-desktop-platforms.yml

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Walkthrough

The PR redesigns the Linux AppImage packaging workflow, replacing the tar.gz compression approach with a full AppDir-based AppImage creation using appimagetool. The workflow now discovers the app root, constructs the AppDir structure with necessary metadata files, and generates a native AppImage artifact.

Changes

Cohort / File(s)	Summary
AppImage Packaging Step .github/workflows/build-desktop-platforms.yml	Renamed and reworked the AppImage packaging step to use appimagetool instead of tar.gz compression. Now downloads appimagetool, creates an AppDir structure with AppRun script and desktop entry, copies the app icon, and generates GitHub-Store-x86_64.AppImage. Updated artifact upload to reference the new AppImage path and set compression level to 0.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

• feat(desktop): Add AppImage + Debian 12 as a target format #239: Modifies GitHub Actions desktop build workflow to add/adjust AppImage packaging steps targeting the same build infrastructure.
• Generate installers #280: Modifies the same workflow file with prior AppImage scaffolding and tarball packaging changes, representing the earlier iteration of this packaging approach.
• ci(workflow): Enhance desktop build process and add Linux variants #238: Updates the same workflow file's Linux packaging and artifact upload steps, adjusting environment variables and artifact naming alongside packaging changes.

Poem

🐰 The AppImage hops forth with grace,
No tar.gz bindings to deface,
AppDir folders neatly arranged,
With appimagetool's magic exchanged,
A swifter package, clean and spaced!

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch generate-installers

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