feat(cv2): remove OpenCV dependency

[Borda]

This pull request removes OpenCV as a runtime dependency and extra from Supervision, making the package rely on its included fallback backend by default. It introduces new release-contract checks, updates documentation to guide users through the migration, and adds CI validation to ensure the wheel works in environments without OpenCV.

Dependency and Packaging Changes

• Removed OpenCV from the dependencies list in pyproject.toml, so Supervision no longer installs or requires any OpenCV distribution by default.

Continuous Integration and Release Checks

• Added a clean-wheel CI job to build, install, and validate the Supervision wheel in an isolated environment without OpenCV, using a new .github/scripts/verify_clean_wheel.py script and a fallback manifest for explicit checks. [1] [2] [3]
• Introduced tests/cv2/test_release.py to assert that OpenCV is not listed as a dependency and that migration documentation is present and up-to-date.

Documentation Updates

• Added a migration guide (docs/how_to/opencv_migration.md) explaining how to use Supervision with or without OpenCV, backend selection, and best practices for different application types.
• Updated the changelog to announce the OpenCV removal, clarify the new backend behavior, and reference the migration guide. [1] [2]
• Updated the FAQ to state that Supervision does not install OpenCV and to link to the migration guide.
• Added the migration guide to the documentation navigation.

---

cc: @robmarkcole
closes #2114

[Copilot]

Pull request overview

This PR removes OpenCV (opencv-python) as a runtime dependency of Supervision so the package defaults to its bundled fallback backend, and adds release/CI guardrails + documentation to ensure the wheel remains usable in environments where cv2 is not installed.

Changes:

• Dropped opencv-python from pyproject.toml (and corresponding lockfile metadata).
• Added a new “clean wheel” CI job plus a wheel verification script + manifest to validate installs in an environment without OpenCV.
• Added/updated documentation (migration guide, FAQ, changelog) and a release-contract test to keep the migration discoverable and prevent OpenCV from reappearing as a dependency/extra.

Reviewed changes

Copilot reviewed 9 out of 10 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
uv.lock	Removes OpenCV from the lock; updates Requires-Dist metadata to match updated deps.
pyproject.toml	Removes opencv-python from runtime dependencies.
tests/cv2/test_release.py	Adds release-contract checks to ensure no OpenCV dependency/extra and that migration docs exist.
tests/cv2/installed_wheel_fallback_manifest.txt	Declares the exact smoke-check contract used by the clean-wheel verifier.
.github/workflows/ci-tests.yml	Adds clean-wheel matrix job and gates the guardian job on it.
.github/scripts/verify_clean_wheel.py	Implements wheel metadata checks + installed-environment smoke probe for fallback behavior.
docs/how_to/opencv_migration.md	New migration guide describing how to run with fallback or an explicitly installed OpenCV wheel.
docs/faq.md	Updates FAQ to state OpenCV is not installed and links the migration guide.
docs/changelog.md	Documents the breaking change and aligns wording/requirements with the new backend behavior.
mkdocs.yml	Adds the migration guide to documentation navigation.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87%. Comparing base (5212af7) to head (75002b3).

Additional details and impacted files

@@           Coverage Diff           @@
##           develop   #2443   +/-   ##
=======================================
+ Coverage       87%     87%   +1%     
=======================================
  Files           85      85           
  Lines        11933   11935    +2     
=======================================
+ Hits         10342   10429   +87     
+ Misses        1591    1506   -85     

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