Implement looking direction indicator for face detection

[Copilot]

Adds visual indicators showing which direction detected faces are looking, using facial landmark analysis.

What's Changed

When faces are detected with facial landmarks, the application now draws a directional indicator line from the face bounding box showing which way the person is looking. The indicator uses five distinct directions:

• Left: Horizontal line from left side of face box
• Slight Left: Diagonal line from bottom-left corner
• Forward: Vertical line from bottom center
• Slight Right: Diagonal line from bottom-right corner
• Right: Horizontal line from right side of face box

Implementation

The direction is calculated by analyzing the position of the nose relative to the center point between the eyes:

float eyeCenterX = (rightEyeX + leftEyeX) / 2f;
float offset = noseX - eyeCenterX;
float ratio = eyeDistance > 0 ? offset / eyeDistance : 0;

This ratio is normalized by the distance between eyes, making it robust across different face sizes and distances from the camera. Direction thresholds are applied to the ratio to determine which of the five directions the face is looking.

Visual Example

Looking Left:              Looking Forward:           Looking Right:
  ────────────────           ────────────────           ────────────────
 │    👁️     👁️   │         │    👁️     👁️   │         │   👁️     👁️    │
━│      👃       │         │       👃      │         │       👃      │━
 │                │         │                │         │                │
  ────────────────           ────────────────           ────────────────
                                   │
                                   │

Features

• ✅ Only draws when facial landmarks are detected
• ✅ Color-coordinated with face bounding boxes
• ✅ Works with multiple faces simultaneously
• ✅ Lightweight calculation with no performance impact
• ✅ Robust error handling

Fixes #[issue_number]

Original prompt

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This section details on the original issue you should resolve

<issue_title>Implement looking direction</issue_title>
<issue_description>We are detecting faces and facial points.
I want to display which way the face is looking, the options are left, slight left, forward, slight right, and right.
For each detected face draw a short line out from the face box either on the left, bottom left corner, bottom, bottom right corner, or right respectively.
When no face points are detected omit this.</issue_description>

Comments on the Issue (you are @copilot in this section)

Fixes #61

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[Keboo]

@copilot rebase on latest master and resolve conflicts

[Copilot]

@copilot rebase on latest master and resolve conflicts

Rebase completed successfully on latest master (commit 459f596). The looking direction feature has been preserved and the conflicts have been resolved. The branch is ready but requires a force push to update the remote.

Changes: 73 lines added to MainWindowViewModel.cs
Build: ✅ Successful (no warnings/errors)
Commit: 5d5a1a0