fix(installer): preserve start type during installs

[Nonary]

Description

Preserve whatever start-type (auto, delayed-auto, demand, or disabled) the Windows SunshineService already uses when the program is upgraded or re-installed.
Previously every update reset the service to Automatic.

Key Points

• Vibe Coding – Most of the code changes and this PR text were AI-generated and then peer-reviewed/tweaked by humans for accuracy and style.
• install-service.bat
  • Reads a marker file written by the uninstaller and re-creates the service with that start-type; defaults to auto on fresh installs.
  • Starts the service only if the preserved mode isn’t disabled.
• uninstall-service.bat
  • Detects the current start-type (or the legacy sunshinesvc) and writes it to %TEMP%\sunshine_start_mode.txt before deletion.
• windows.cmake
  • Removes installation of the obsolete autostart folder and call to autostart-service.bat.
• autostart-service.bat – Deleted (logic folded into the installer scripts).

Screenshot

Not applicable – no UI changes.

Issues Fixed or Closed

• Closes #3469

Type of Change

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature
• [ ] Breaking change
• [ ] Dependency update
• [ ] Documentation update
• [ ] Repository update

Checklist

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have added or updated the in-code documentation blocks for new or existing scripts

[sonarqubecloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud