Make crossing comparisons shareable and measurable

[sbc1-code]

Purpose

Make the San Ysidro–Otay Mesa comparison easier to share with border-crossing friends and learn whether it helps someone choose a crossing.

Change

• Add WhatsApp and copy-link actions on comparison pages. Shared URLs open the current data instead of preserving an old wait-time claim.
• Add a three-choice, anonymous usefulness prompt. Umami receives only a canonical pair and a fixed answer.
• Record the new events and pilot interpretation in the existing repo documentation.

This uses the current hosting and analytics stack. It adds no account, database, paid API, or recurring service. It does not change the free waits or Adsterra behavior.

Evidence and interpretation

The current Umami readout showed two compare-open events in the last seven days. That is too little to judge the new comparison. compare-feedback is a stated opinion, not proof of an actual crossing or a paid business need. Review results after a friend pilot and the existing 30-day window.

Review status

Static diff and whitespace inspection completed. Automated test suites were not run in this task; GitHub checks may run on the PR. Production remains on the existing GitHub Pages deployment pending owner review.

Related: #101