Add Web quality overview

[Axelxrd]

Summary

• add a Web adaptation quality overview for chapter coverage, dialogue ratio, lowest coverage score, and risk count
• render responsive overview meters in the inspector without changing API/export formats
• document the Web quality overview and guard it in static asset smoke checks

Validation

• node --check src\novel2script\web\static\app.js
• python -m pytest tests\test_web.py tests\test_packaging.py -q --basetemp .pytest-tmp-web-quality-focused3
• python -m ruff check .
• python -m pytest -q --basetemp .pytest-tmp-web-quality-final
• python scripts\smoke_web_server.py
• git diff --check
• Edge + puppeteer-core browser check: sample conversion updates quality overview and mobile 390px viewport has no horizontal overflow