chore: remove unused repository assets

[DavidYang0429]

What changed

• remove two intermediate design-comparison screenshots
• remove 20 legacy theme/demo assets that have no source references
• remove the obsolete commented background-image styling
• ignore local Playwright CLI artifacts and update the design QA inventory

Why

The tracked repository was dominated by unused image assets. This keeps all active instructional screenshots, final design references, historical course material, and archived comment data while reducing the checked-out tracked footprint from 16.10 MiB to 9.18 MiB.

Impact

• 22 unused tracked files removed
• approximately 6.92 MiB removed from the current tree (about 43%)
• no route, course content, comment mapping, PWA asset, or active UI asset removed

Validation

• pnpm docs:check
• VuePress build: 101 pages
• internal link check: 4,787 links
• git diff --check
• BIS source registry validation: 16 entries

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Project	Deployment	Actions	Updated (UTC)
mscbis	Ready	Preview, Comment	Jul 28, 2026 5:33am