chore: Update electron-builder v26.0.3

[jeanfbrito]

🔐 Security Enhancement: Electron-Builder v26.0.3 + ASAR Integrity Protection

Upgrades electron-builder to v26.0.3 and implements ASAR integrity validation to prevent malicious app.asar replacement attacks (e.g., Loki C2, MITRE ATT&CK T1218.015).

✅ Security Improvements

• EnableEmbeddedAsarIntegrityValidation: true (blocks malicious ASAR files)
• OnlyLoadAppFromAsar: true (prevents external code injection)

🎯 Smart Implementation

• Regular builds: Full ASAR integrity protection applied
• Mac App Store builds: Fuses skipped for compatibility (App Store provides own validation)
• Cross-platform: Proper executable paths for Windows (Rocket.Chat.exe), Linux (rocketchat-desktop), macOS (Rocket.Chat.app)

🛠️ Technical Changes

• Updated electron-builder: 25.1.8 → 26.0.3
• Added conditional afterPack hook for platform-specific fuse application
• Removed deprecated parameters: publisherName, signDlls, StartupWMClass, MimeType
• Updated GitHub Actions release workflow for MAS compatibility

Closes: CORE-1069 - Protects against documented Electron security vulnerabilities while maintaining all distribution channels.

https://rocketchat.atlassian.net/browse/CORE-1069