feat(web): spatial platform picker (map + walk-sorted list)

[i11v]

What & why

Prague interchanges (Anděl = 9 platforms around one junction) are the product's hard case. Today a stop card offers an "All / nást. A / nást. B…" chip filter — it names a platform but never says where to stand. This replaces it (where wired) with a shared map + walk-sorted platform list picker: one tappable pin per platform beside a list sorted by walk time, kept in sync, surfaced on both surfaces — the stop card and inline in each search result.

How it's built

GTFS stops.txt (lat/lon per platform row)
   │  scripts/lib/build.ts — keep per-platform coords
   ▼
contract: StopPlatform { code, stop, lat, lon }
   ▼
lib/platforms.ts  buildPlatformPicks(platforms, origin, departures?)
   • join index platform.code === departure.platform (raw → metro matches)
   • walk via haversineMetres / metresToWalkMinutes; sort by walk, then code
   ▼
PlatformPicker (variant "sheet" | "inline")
   │  React.lazy → <Suspense>
   ▼
RealMap (Leaflet, dark CARTO tiles, divIcon pins)
   ├─ StopCard  (sheet, live countdowns)   ← App.tsx threads platforms/origin/onPick
   └─ search.tsx ResultCard (inline, no countdowns)

• Data layer: StopPlatform gains lat/lon; build.ts keeps each platform's own GTFS coords instead of averaging them into the node centroid. The index is a gitignored build artifact, regenerated at deploy — no committed-data change.
• lib/platforms.ts: pure buildPlatformPicks joining index geo with the live board (raw platform === code so per-line metro codes match), sorted nearest-first. Reuses existing haversineMetres/metresToWalkMinutes/reachTier/Origin.
• RealMap.tsx: static dark Leaflet map, divIcon pins (no broken default-marker PNGs), "you" marker, dashed line to the selected pin, two-way onSelect. Default-exported and React.lazy'd — lands in its own chunk.
• PlatformPicker.tsx: map + walk-sorted list reusing RouteChip/VehicleIcon/Count. sheet adds a confirm bar; inline adds per-row "Add" + "Add whole stop".
• Integration: MapIcon; StopCard gains optional platforms/origin/onPick/onWholeStop (chip filter stays as the fallback when absent, e.g. preview.tsx); App.tsx threads them and re-scopes a card in place; search.tsx ResultCard gets an expandable inline picker.

Behaviour notes

• No geo: map still renders, rows fall back to code order, walk shows "—".
• Search results aren't subscribed → inline picker shows code + walk only (no countdowns). Accepted caveat.
• Single-platform stops: no map button, unchanged.

Verification

• bun run typecheck — clean (the TS11 messages are pre-existing Effect-LS info diagnostics in the untouched worker package).
• bun run test — 74 passing, incl. updated build.test.ts (per-platform coords) and a new platforms.test.ts (sort order, metro raw-code join, null-origin).
• bun run build:web — succeeds; Leaflet is a separate chunk (RealMap-*.js ~152 kB + RealMap-*.css ~15 kB) loaded only when a picker opens.
• ⚠️ bun run build:index and interactive bun dev smoke could not run here — outbound fetch to data.pid.cz is blocked by the environment network policy (HTTP 403) and there's no cached GTFS. The index regenerates at deploy; the build logic + schema-decode are exercised by build.test.ts. Manual smoke (map button → pick narrows card → re-open switches; search expand → add a platform; geo-off degrade) is still worth a pass in a networked env.

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Generated by Claude Code

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