[turinglambdaai]

Why

Across the product portfolio, screenshots are useful but cannot own user workflows, availability or commercial claims. This is the first reviewable implementation slice for portfolio docs issue #5; the broader homepage redesign stays in issue #2.

What changed

• New full English/Chinese public-presentation standard covering site vs README vs guide responsibilities, source-of-truth, screenshots as versioned evidence (real versus mockup), alt/caption, release-triggered review and deployed/source reconciliation.
• Paired README navigation to the standard and explicit “not yet audited” boundary.
• A dependency-free Python static check for the front door: required entry points, local assets, missing alt attribute, duplicate IDs, invalid relative paths and broken in-page fragment links.
• Minimal GitHub Actions PR/push job for the check. Does not add a website framework or alter the live page.

Verification and boundaries

• Audit base: 79a2b705a37a8c428c3d1a184d9f331d66624361. Reviewed AGENTS.md, PORTFOLIO.md, docs/PRODUCT-STANDARD.md, docs/DOCUMENTATION-LANGUAGES.md and docs/HOME-PAGE-PLAN.md before change.
• An initial source-content review found existing index.html has 5 distinct IDs, 5 in-page references with targets and one local image with alt; the local assets were confirmed under assets/img, assets/css and assets/fonts.
• Not claimed: all image freshness/EN-ZH equivalence verified, all product sites migrated, deployed jrtx.site matches commit, CI already green, visual/mobile/a11y or product acceptance passed. Follow-up product issues/PRs own these.
• Rollback: revert this one docs/check commit; it has no runtime/landing page change.

Closes no broad portfolio issue; this establishes its Phase A standard and automated structural baseline.