Add route-explorer.com integration: connection finder + departures board

- RouteExplorerClient: anonymous HMAC token (route-explorer.com/api/token,
  IP rate-limited 10/min), POST /api/flight-search with X-API-Token; auto
  retry on 401/403 token rotation. Wraps the SuperJSON {json:{...}} envelope
  for the upstream tRPC endpoints.
- RouteExplorerModels: Codable types for /route, /departures responses
  (RouteConnection, RouteFlight, cabins, appendix). Custom ISO-8601
  decoder for the dateTime-with-offset timestamps. Bridge helper
  RouteFlight.toFlightSchedule(...) so route-explorer legs reuse the
  existing FlightLoadDetailView and AirlineLoadService flow for
  supported carriers (UA/AA/NK/KE/B6/AS/EK/XE).
- RoutePlannerView: feature (a) — direct + multi-stop A→B routing via
  /route with maxStops 0/1/2, sortBy departure_time/duration, optional
  interline-only filter. Renders one ConnectionRow per itinerary with
  chained legs and layover indicators.
- WhereToGoView: feature (b) — "where can I go" departures board for an
  airport over a 2/4/6/12/24h window. Capacity pills (F/J/W/Y), color-
  coded countdown, cross-midnight rollover. Tap any leg → load detail.
- IATAAirportPicker: lightweight local-only picker against
  AirportDatabase (no flightconnections roundtrip needed since
  route-explorer keys on IATA, not FC IDs).
- ContentView: two new entry-point cards (Find Connections, Where can I
  go?) above the favorites list.
- api_docs/route_explorer_api.md + captures: full endpoint reference and
  representative response samples (DFW→LAS direct, DFW→KOA 1-stop,
  LBB→KOA 2-stop, AA2178 schedule, DFW departures).

No tests yet — project has no test target and adding TDD would require
scaffolding XCTest first. Worth backfilling tests for the date decoder,
layover math, and toFlightSchedule bridge using the saved fixtures.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

api_docs/route_explorer_captures/flight_AA2178.json

@@ -0,0 +1,67 @@
+{
+  "json": {
+    "flights": [
+      {
+        "flightNumber": 2178,
+        "flightSuffix": null,
+        "departure": {
+          "airportIata": "DFW",
+          "dateTime": "2026-05-01T16:45:00-05:00",
+          "terminal": "0"
+        },
+        "arrival": {
+          "airportIata": "LAS",
+          "dateTime": "2026-05-01T17:46:00-07:00",
+          "terminal": "1"
+        },
+        "durationMinutes": 181,
+        "equipmentIata": "32Q",
+        "serviceType": "J",
+        "isCodeshare": false,
+        "stops": 0,
+        "stopCodes": null,
+        "totalSeats": 196,
+        "classes": {
+          "first": {
+            "seats": 0,
+            "mealCodes": []
+          },
+          "business": {
+            "seats": 20,
+            "mealCodes": [
+              "D"
+            ]
+          },
+          "premiumEconomy": {
+            "seats": 0,
+            "mealCodes": []
+          },
+          "economy": {
+            "seats": 176,
+            "mealCodes": [
+              "R",
+              "D"
+            ]
+          }
+        },
+        "inFlightService": [
+          12,
+          18,
+          22,
+          23,
+          24,
+          26,
+          27,
+          28,
+          29,
+          31
+        ],
+        "id": "AA_2178_DFW_2026_05_01",
+        "carrierIata": "AA",
+        "carrierIcao": "AAL",
+        "isWetlease": false,
+        "codeshares": []
+      }
+    ]
+  }
+}