[caumeira]

What changed

Add native crosshair control for the Alienware AW3225QF on Windows using DDC/CI. The monitor appears as a device with a companion Crosshair page in nexus-web.

Companion UI change: nexus-web PR #3.

• Recognize AW3225QF through the physical monitor description or EDID name.
• Read the active AlienVision engine through VCP 0xEC. Apply style, color and mask using the Gen1 0xED sequence, with retries and serialized requests.
• Save the last selection per display because 0xED cannot be read back. Respect the existing DDC/CI opt-out.

Support is restricted to AW3225QF. Other Alienware models have not been validated. This controls the monitor's native crosshair, not a software overlay.

Hardware validation

• Device: Alienware AW3225QF
• VID:PID: Not used; control is through the video connection, not USB RGB.
• Firmware: Not recorded.
• OS: Windows
• Commit tested: Initial development version. Final integrated build awaiting confirmation.
• Observed: The contributor confirmed that Enabled, styles, colors and sizes work on their AW3225QF.

Not tested: Other Alienware models; they are not enabled by this implementation.

Tests

• Service build passed with 0 warnings and 0 errors.
• 17 new controller tests passed in isolation: command encoding, delays, retries, validation, opt-out, concurrent requests, cancellation and saved selections.
• The existing complete test project cannot compile on Windows because unrelated diagnostics/update tests call constructors with missing arguments. Isolation used a temporary MSBuild target outside the repository; it is not part of this PR.

CLA

• I have read and agree to CLA.md.