Add native Windows Arm64 library readiness

[yeelam-gordon]

Scope: Windows Arm64 pre-action readiness

This PR makes libopenshot and its Python binding build- and test-ready for native Windows Arm64. It does not publish or sign an OpenShot release.

Changes

• CLANGARM64 GitLab lane and GitHub-hosted windows-11-arm presubmit
• exact consumption of the matching OpenShotAudio PR branch/artifact
• fail-closed native-host, package-lock, and recursive PE validation
• corrected native (UNKNOWN, ARM64) process oracle
• FFmpeg 8/9, OpenCV 5, ImageMagick 7, Ninja, and Windows test portability fixes required by the native toolchain

Evidence

• native Arm64 library and Python binding compile successfully
• native full CTest passed 519/519 on the available Arm64 machine
• current hosted Arm64 CI passed before the upstream-baseline merge; refreshed CI is running
• validator tests and Linux matrices pass

Dependency

Requires OpenShot/libopenshot-audio#171.

Post-actions owned by maintainers

Production artifact promotion, signing, publication, and official support announcement.

AI assistance disclosure: implementation and review used GitHub Copilot CLI.

[yeelam-gordon]

Automated review is being run on mirror PR yeelam-gordon#1. Findings and fixes are pushed to this same head branch. This PR depends on OpenShot/libopenshot-audio#171.

[yeelam-gordon]

Hosted Windows Arm64 CI now compiles the complete library and runs 516 tests; 512 pass. The remaining four failures are isolated dependency-runtime follow-ups (FFmpeg 9 spherical metadata and ImageMagick 7 ImageWriter crashes), documented on the mirror review PR: yeelam-gordon#1. The copilot-pr-autopilot round-cap circuit breaker stopped further scope expansion after all Arm64 lane/build blockers were resolved.

[yeelam-gordon]

Latest hosted Windows Arm64 evidence: the complete library, Python binding, FFmpeg 9/OpenCV 5 compatibility code, examples, and all 516 test executables compile successfully. CTest passes 512/516. Remaining explicit follow-ups are two FFmpeg 9 spherical-metadata round-trip tests and two ImageMagick 7 ImageWriter crashes. The automated review loop stopped at its round-cap circuit breaker with zero open threads rather than hiding or disabling these dependency-runtime failures.