Wire the contribution leaderboard, city switcher and home distance into their pages - #335

What this changes

Part of #313. Wires three of the standalone components that no page imported yet; each checkbox below is a separate item in that issue.

• ContributionLeaderboard on /about (src/app/about/page.tsx): ranks added_by across the dataset already loaded on that page, no new data or API.
• CitySwitcher in the homepage hero (src/components/home/hero.tsx): "Jump to a city" going to /city/<slug>, fed by the getCities(places) the hero already computes.
• RouteEtaCard in the pin popup: PlacesMap now passes the signed-in visitor's saved home ({ lat, lng }) to MapView, which passes it to ClusteredMarkers and PinPopup. With a home set, the popup shows the straight-line distance and a rough walking time; without one it renders nothing.

Not touched, and why: PlaceReviewBadge and RecentAdditionsFeed need data the schema does not have (ratings, added-on dates); HeatmapToggle needs map rendering first; PlaceDetailDrawer, ComparePlacesSheet, SharePlaceCard and PlacePhotoGallery need a design decision on where they open from; CategoryIcon would change the pin-matching legend dots. #313 therefore stays open.

Proof

• New tests: pin-popup.test.tsx (+2: distance shown with a home, nothing without), about/page.test.tsx (leaderboard heading renders), home/hero.test.tsx (the jump-to-city combobox is present).
• npm run typecheck, npm run lint: clean. npm run test:unit: 72 files, 663 tests pass.
• This branch includes the one-test fix from Fix main: pass the new PlacesMap props in the filter presets test #334 (main currently fails typecheck without it); that commit drops out of the diff once Fix main: pass the new PlacesMap props in the filter presets test #334 merges.

Not verified

I did not open the pages in a browser, so the layout of the new switcher in the hero and the extra popup line on a small screen are unchecked; the tests cover rendering and props only.

Type of change

• Code or fix
• New public place(s)
• New or updated benefit guide
• New or updated resource link
• Docs