Lead the home screen with the rider's own mountains

[greenido]

Why

A returning rider landed on the hero, pass filter, units switch, view tabs, search, a location button and then a large welcome card with no data in it. Their favorites were hidden behind a star button.

What

• HomePicks (new) on the home screen, directly below search:
  • With favorites: "Your mountains today". Up to 6 favorites, ranked by today's Ride Score. Each row shows the 24h snow and its best day this week, taken from the planner's mid-mountain outlook so it matches the grid. There's also a link to the full favorites comparison.
  • Without favorites: "Top picks today". It takes the 6 biggest resorts in the region the browser's time zone points to and shows the best 3, plus a "See all" link into Compare.
• regionForTimezone() in lib/regions.ts, with a new tests/regions.test.ts:
  • It needs no permission prompt and puts nothing in the URL.
  • If the guessed region has no resorts (for example after a pass filter, or Scandinavia, which has none yet), it falls back to the first available region.
  • The time zone is read after mount so the static prerender can't bake in the build machine's zone.
• The empty welcome card is replaced by its one useful line: the resort count and the credit.

Testing

• tsc --noEmit, next lint and all 10 offline test suites pass, including the new regions suite.
• 375×812, no favorites: shows "Top picks today · US West" (the browser is set to America/Los_Angeles).
• 375×812, 3 favorites: shows the favorites ranked, with "best Mon (54)" on Zermatt. Tapping a row opens the resort and Back returns home. No console errors.
• 1440×900: the list is capped to the search bar's width.

Merge order

This is 3 of 3. I merged #13, #14 and this PR onto main in that order on a scratch branch: all three merged without conflicts (git auto-merged app/page.tsx, where #13 and this PR touch different parts). On the combined result, lint, typecheck, all 10 test suites and next build pass.

🤖 Generated with Claude Code