heroic: add linux AppImage support

[PrudviTeja99]

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After making any changes to a cask, existing or new, verify:

• The submission is for a stable version or documented exception.
• brew audit --cask --online <cask> is error-free.
• brew style --fix <cask> reports no offenses.

Additionally, if adding a new cask:

• Named the cask according to the token reference.
• Checked the cask was not already refused (add your cask's name to the end of the search field).
• brew audit --cask --new <cask> worked successfully.
• HOMEBREW_NO_INSTALL_FROM_API=1 brew install --cask <cask> worked successfully.
• brew uninstall --cask <cask> worked successfully.

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• I did not use AI/LLM to create this PR, or I disclosed the tool/model below and reviewed its output, including zap stanza paths; I did not attribute commits to AI and will answer maintainer questions and review comments myself without AI/LLM.

AI (Antigravity) assisted in structuring the multi-OS conditionals. All changes, URLs, and the AppImage SHA256 checksum were personally reviewed, calculated, and verified against official upstream downloads.

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