Expand QR generator print guidance

[rrih]

Summary

• Adds QR code print-size guidance for business cards, flyers, handouts, posters, and signs.
• Adds pre-publication checks for destination validation, printed-surface testing, and fallback URLs.
• Keeps ad density unchanged and preserves the existing QR generator workflow.

Selected action

• Revenue accelerator action: existing-page-expansion
• Target: https://rrih.github.io/tools/qr-generator/
• Automation mode: auto-pr

Expected KPI impact

• Improves long-tail usefulness and search content depth on a page currently reported with 1 impression and 0 clicks in the latest accelerator snapshot.
• Gives visitors practical print/deployment guidance, which should improve task completion and reduce bounce on QR-related traffic.

Data rationale

• data/growth/accelerator/latest.json lists QR Generator expansion as a low-risk auto-pr candidate.
• Existing draft PRs Improve animation generator CTR copy #26 and Add overtime pay calculator #28 are both draft/CLEAN/CI success, so this stays within the three open revenue-growth PR limit.

Verification

• bash /Users/rrih/.codex/skills/rrih-github-io-revenue-accelerator/scripts/github_preflight.sh rrih/rrih.github.io: success on attempt 1/4
• bun test: 27 pass
• bun --bun tsc --noEmit: pass
• bun run lint: pass with existing 9 warnings
• bun run build: pass, 189 static pages generated
• bun run dev-check: pass, dev server reached Ready and was stopped
• Browser check: /tools/qr-generator/ shows the new sections at 1280px and 390px, no horizontal overflow, no console errors

Refs #15