Remove fallbacks and add explicit tag family parameter in AprilTag detection

[Copilot]

Addresses review feedback on #542 to remove defensive fallbacks and verify pose detection math.

Changes

Removed fallbacks:

• Direct import of pupil_apriltags (raises ImportError if missing)
• load_camera_intrinsics() propagates FileNotFoundError
• detect_apriltag_pupil() raises FileNotFoundError for missing images
• Removed pd.Timestamp.now() fallback in JSON export

Explicit tag family:

• Added --tag-family CLI argument (default: tag36h11)
• Removed multi-family fallback loop that tried 4 families sequentially

python detect_apriltag.py img.png --tag-family tag36h11

Math verification:
Cross-checked against pupil-apriltags docs — implementation is correct:

• Camera params: [fx, fy, cx, cy] from intrinsic matrix
• Tag size in meters
• Euler angles via R.from_matrix(pose_R).as_euler('xyz', degrees=True)

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[sgbaird]

@copilot also, you shouldn't archive any of those files.

[Copilot]

@copilot also, you shouldn't archive any of those files.

The archive folder and file renames appear to be from the parent PR #542 (commit 00c0117), not from my changes in this sub-PR. My commits only modified CHANGELOG.md and detect_apriltag.py to remove fallbacks and add the --tag-family parameter. Should I revert the archive changes in the parent PR #542?