Remove Spirit Airlines (defunct — merged into Frontier)

Spirit ceased operations, so the fetchSpiritStatus path and all NK
references are dead code. Pulled out:

- AirlineLoadService: drop `case "NK"` from the router, delete
  fetchSpiritStatus (the GetFlightInfoBI POST that was returning 403
  even after our APIM key was accepted).
- FlightLoadDetailView: drop the `schedule.airline.iata == "NK"` branch
  and the spiritUnavailableView placeholder.
- FlightLoad model: update the airlineCode comment.
- AirlineLoadIntegrationTests: remove test_NK_spirit and drop "NK" from
  statusOnlyAirlines / knownDailyFlights fallback table.
- AIRLINE_INTEGRATION_GUIDE.md: tombstone the Spirit section and remove
  it from the cheat-sheets and recommendations.

Test suite now: 6 airlines passing (AA, AS, B6, EK, KE, UA), 1 skipped
(XE — WKWebView host required), 0 failures, runs in ~10s.

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

AIRLINE_INTEGRATION_GUIDE.md

@@ -12,7 +12,7 @@ Drop-in reference for integrating flight load / seat availability data from 11 a
 | B6 | ✅ Status-only | Confirms flight exists; no load data without check-in session |
 | EK | ✅ Status-only | Confirms flight exists; load data requires PNR |
 | KE | ✅ Working | Returns seat count only (no capacity) |
-| NK | ❌ Broken (2026-05-26) | `GetFlightInfoBI` returns HTTP 403 with `{"getFlightInfoBIResult":null}`. APIM key is still accepted (401 without it), but the call itself is now rejected. Likely endpoint deprecation or new auth requirement. Spirit APK in `airlines/com.spirit.*` may have the new shape. |
+| ~~NK~~ | Removed | Spirit Airlines ceased operations (merged into Frontier). Removed from `AirlineLoadService` and tests. |
 | XE | Manual only | WKWebView path; unit tests can't exercise it |
 
 ---
@@ -208,23 +208,9 @@ Script ready at `scripts/jsx_availability.js`.
 
 ---
 
-## 5. Spirit Airlines — PARTIAL (status only, no standby)
+## 5. ~~Spirit Airlines~~ — DEFUNCT
 
-**What you get:** Flight status, station/route data. **No standby — Spirit is a ULCC and doesn't run standby lists.**
-
-**Auth:** Static APIM key (decrypted). Plain curl for GETs; POSTs mostly blocked by Akamai CyberFend sensor.
-
-**Key:** `c6567af50d544dfbb3bc5dd99c6bb177`
-
-```bash
-curl -X POST "https://api.spirit.com/customermobileprod/2.8.0/v3/GetFlightInfoBI" \
-  -H "Ocp-Apim-Subscription-Key: c6567af50d544dfbb3bc5dd99c6bb177" \
-  -H "Content-Type: application/json" \
-  -H "Platform: Android" \
-  -d '{"departureStation":"FLL","arrivalStation":"ATL","departureDate":"2026-04-08"}'
-```
-
-Seat maps require JWT + CyberFend sensor data (real device + Frida hook only).
+Spirit ceased operations and merged into Frontier. Removed from the codebase entirely. Section retained as a placeholder so the numbering below doesn't shift.
 
 ---
 
@@ -356,7 +342,6 @@ Same backend powers Lufthansa, SWISS, Austrian, Brussels.
 |------------|--------------------|---------|
 | Alaska     | APIM key header    | Lowest (curl works) |
 | Emirates   | none               | Lowest (curl works) |
-| Spirit     | APIM key (GET only)| Low (curl works) |
 | JetBlue    | apikey header      | Low (curl works) |
 | Korean Air | `channel` header   | Low (Playwright or curl) |
 | JSX        | Playwright → JWT   | Medium |
@@ -382,7 +367,6 @@ These four are the core of any flight-load product. Alaska is the easiest to int
 
 ## Tier 2: Status only (useful, but no seat data)
 
-- **Spirit** — status/routes, no standby (ULCC)
 - **Emirates** — status, zero auth
 - **Korean Air** — status; `flightSeatCount` returns 0 far out
 - **JetBlue** — status + route DB; loads need PNR
@@ -399,7 +383,7 @@ These four are the core of any flight-load product. Alaska is the easiest to int
 3. Layer in American for the third major US carrier.
 4. JSX as a bonus — only route pairs that JSX serves (private terminals).
 5. For Delta/JetBlue: show flight status only, note "seat data unavailable" unless you have a PNR.
-6. Use Emirates/Korean Air/Spirit for status on international/ULCC routes.
+6. Use Emirates/Korean Air for status on international routes.
 
 ## Shared integration notes