build: switch opencv-python to opencv-python-headless

[halfcrazy]

Motivation

MinerU only uses cv2 for image processing (no GUI APIs like imshow/ waitKey), so the headless build is functionally identical while dropping the libGL.so.1 system dependency that breaks installs in minimal/server environments. libgl1 is therefore also removed from both Dockerfiles.

Modification

Switch opencv-python to opencv-python-headless

Related PaddlePaddle/PaddleOCR#8414

Checklist

Before PR:

• Pre-commit or other linting tools are used to fix the potential lint issues.
• Bug fixes are fully covered by unit tests, the case that causes the bug should be added in the unit tests.
• The modification is covered by complete unit tests. If not, please add more unit test to ensure the correctness.
• The documentation has been modified accordingly, like docstring or example tutorials.

After PR:

• If the modification has potential influence on downstream or other related projects, this PR should be tested with those projects.
• CLA has been signed and all committers have signed the CLA in this PR.

I have read the CLA Document and I hereby sign the CLA

[github-actions]

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[halfcrazy]

I have read the CLA Document and I hereby sign the CLA