Use relative imports in UAV CV helpers

[ethayu]

Summary

• Convert legacy UAV CV helper imports to package-relative imports.
• Guard failed video reads in the legacy tracker helper.
• Skip contour conversion/confidence when the helper does not find a contour, and pass image dimensions via frame.shape.

Verification

• source /opt/ros/humble/setup.bash && export PYTHONPATH=$PWD/controls/sae_2025_ws/src/uav:$PYTHONPATH && npx --yes pyright controls/sae_2025_ws/src/uav/uav/cv/calibrate.py controls/sae_2025_ws/src/uav/uav/cv/track.py --outputjson
• python3 -m compileall controls/sae_2025_ws/src/uav/uav/cv/calibrate.py controls/sae_2025_ws/src/uav/uav/cv/track.py
• ruff check controls/sae_2025_ws/src/uav/uav/cv/calibrate.py controls/sae_2025_ws/src/uav/uav/cv/track.py
• ruff format --check controls/sae_2025_ws/src/uav/uav/cv/calibrate.py controls/sae_2025_ws/src/uav/uav/cv/track.py

Refs #208
Part of #201

[ethayu]

Folded into #237 as a separate commit; closing to keep CV/vision typing in one PR.