The seller report shows how the home was shown: the number of showings, what buyers' agents said, and how many people signed in at open houses #141

Intent: the one-page seller report (/listings/:id/report) tells the seller what went out but not who came, and activity is what a seller asks first.

Done looks like:

• [ ] The seller report has an Activity section after the result line: the number of showings logged, the number of open house visitors who signed in, and up to the five newest pieces of buyer-agent feedback, each with its day, in the order they were logged (newest first).
• [ ] The report shows counts only for visitors — never a visitor's name or email, since the seller sees the report.
• [ ] With no showings and no visitors the section says so in one plain sentence rather than showing zeros in a table.
• [ ] The 412 Alder Lane sample (or whichever sample has showings) shows a filled Activity section, so the meeting shows it.
• [ ] Feedback text is escaped; the section prints on the same one page as today (print styles kept).
• [ ] Tests: a report for a listing with two showings and three visitors says 2 and 3 and shows the feedback; a report never contains a visitor's email; an empty listing shows the plain sentence. bun test and bun scripts/design-lint.ts pass.
• [ ] README's seller report paragraph mentions the activity.

Files I expect: src/report.ts, src/pages/report.ts, src/showings.ts or src/visitors.ts (read-only helpers), src/sample.ts, src/report.test.ts, README.md.

Risks: the open pull for #103 adds showings to the weekly seller update; reuse its counting helper if it has landed, and keep the two from disagreeing on what counts as a showing.

Suggested crew: a builder.