feat(vdd): add virtual display management

[fatebugs]

Description

Integrate Parsec VDD to enable dynamic virtual display management on Windows. This allows Sunshine to create and manage virtual displays without requiring a physical monitor, which is essential for headless streaming setups.

Key changes

• VDD Core (vdd_control.cpp/h): Virtual display lifecycle management — create, remove, enumerate displays, and handle display mode/resolution configuration
• Configuration (config.cpp/h): New VDD configuration options (enable/disable, adapter selection, display count, resolution presets)
• REST API (confighttp.cpp): Endpoints for runtime VDD control (add/remove display, query status)
• Startup (main.cpp): Automatic VDD initialization on service start when enabled
• System Tray (system_tray.cpp): Quick VDD controls in tray menu
• Web UI (VirtualDisplay.vue): Full management panel for virtual displays with add/remove/resolution controls
• Web UI integration (AudioVideo.vue, config.html): Navigation and display area integration
• i18n (en/zh/zh_TW): Full translations for all VDD-related UI strings
• Build (cmake + third-party/parsec-vdd): VDD header integration, compile definitions

Screenshot

Issues Fixed or Closed

• N/A

Roadmap Issues

• N/A

Type of Change

• feat: New feature (non-breaking change which adds functionality)
• fix: Bug fix (non-breaking change which fixes an issue)
• docs: Documentation only changes
• style: Changes that do not affect the meaning of the code (white-space, formatting, missing semicolons, etc.)
• refactor: Code change that neither fixes a bug nor adds a feature
• perf: Code change that improves performance
• test: Adding missing tests or correcting existing tests
• build: Changes that affect the build system or external dependencies
• ci: Changes to CI configuration files and scripts
• chore: Other changes that don't modify src or test files
• revert: Reverts a previous commit
• BREAKING CHANGE: Introduces a breaking change (can be combined with any type above)

Checklist

• Code follows the style guidelines of this project
• Code has been self-reviewed
• Code has been commented, particularly in hard-to-understand areas
• Code docstring/documentation-blocks for new or existing methods/components have been added or updated
• Unit tests have been added or updated for any new or modified functionality

AI Usage

• None: No AI tools were used in creating this PR
• Light: AI provided minor assistance (formatting, simple suggestions)
• Moderate: AI helped with code generation or debugging specific parts
• Heavy: AI generated most or all of the code changes

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[fatebugs]

@ReenigneArcher What else do I need to do to merge this PR into the master?

[sonarqubecloud]

Quality Gate failed

Failed conditions
1 New issue
1 New Code Smells (required ≤ 0)

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[neatnoise]

That is useful for headless setups. I tried it out.
Few remarks when headless setup was used:

• I managed to make it work by setting manually these vars (I couldn't set vdd_enabled and vdd_refresh_rate via gui):

vdd_display_count = 1
vdd_enabled = 1
vdd_refresh_rate = 60

• I had to force right adapter with adapter_name setting
• I had an issue to save display settings via sunshine gui. It got lost after the sunshine restart even when display was added and clicked "Save" + "Apply"
• I suggest to add some information about the parsec VDD installation requirement and links to the drivers.