🔒 Add signature verification for downloaded updates

[hatimhtm]

🎯 What: The app lacked code signature verification for downloaded updates before copying them to /Applications. This meant a malicious actor could intercept the download (e.g., man-in-the-middle attack or compromised release asset) and inject a tampered DMG, which the app would blindly install and execute.

⚠️ Risk: This vulnerability allowed for arbitrary code execution with the permissions of the user. Once the malicious update is installed and launched, it could harvest data, establish persistence, or further compromise the system.

🛡️ Solution: Added a codesign verification step using Process immediately after mounting the DMG. By running /usr/bin/codesign --verify --deep --strict appSourceURL.path, we ensure the update has not been tampered with. Only if codesign returns a 0 termination status will the app proceed to replace the existing installation. Otherwise, it gracefully falls back to opening the manual download page in the browser.

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PR created automatically by Jules for task 14711124232905774496 started by @hatimhtm

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