Add video step-overlay walkthrough report

[JE-Chen]

Reporting batch — the visual companion to the HTML/JSON reports. Full layers + tests + EN/Zh v39 docs + README.

Feature (utils/video_report, cv2 only on the real path)

• write_step_video(steps, output, fps, seconds_per_step): renders per-step screenshots into a walkthrough video where each frame is held for a few seconds with its caption and a pass/fail colour banner burned in. build_overlay_plan (per-step frame plan, no I/O) and render_overlay_frame (single banner) are usable on their own.
• Testable without cv2: the loader / drawer / writer_factory hooks are injectable, so the assembly logic is unit-tested with fakes and no cv2/numpy dependency (runs in quality.yml). The real path lazily imports cv2 only when those hooks are absent; a dedicated test exercises it under importorskip. The writer is released in a finally.
• Executor AC_write_step_video (steps as list or builder JSON string); MCP ac_write_step_video; Builder under Report.

Verification

• 8 tests pass (frame plan, min-1-frame, injected drawer, full assembly with fakes, writer released on error, real OpenCV path under importorskip, wiring, facade); ruff clean; radon no CC≥C; bandit clean; PySide6-free.

[codacy-production]

Up to standards ✅

🟢 Issues 0 issues

Results:
0 new issues

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🟢 Metrics 43 complexity · 0 duplication

Metric	Results
Complexity	43
Duplication	0

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud