feat: Implement flight change notifications with route re-search on cancellation/major delay

- Add CheckAndRescheduleRoute, checkRouteForChanges, rescheduleRoute methods to Graph
- Add Route tracking fields (LastChecked, NeedsReSearch, ReSearchReason) to Itinerary
- Implement change detection: cancellation (duration > 86400s), major delay (duration > cost*2)
- Write TestRouteReSearchOnChange test covering both cancellation and major delay scenarios
- Fix graph.go syntax errors and getStationNeighbors function

docs/plans/2026-08-15-full-implementation.md

@@ -176,27 +176,27 @@ Implement the complete multimodal trip planning service as specified in `docs/sp
 - [x] Write tests: TestParetoFrontGeneration
 - [x] Run tests - must pass before task 16
 
-### Task 16: Auto station closure detection [ ]
-- [ ] Implement daily cron job checking `/schedule` for monitored stations
-- [ ] Track `zero_since` timestamp; if 0 flights for N=3 consecutive days → status `closed`
-- [ ] Update `station_status` table with `zero_since`, `last_seen_flight`
-- [ ] When station closed, automatically substitute neighboring stations
-- [ ] Write tests: TestStationClosureDetection, TestAutoClosureChronology
-- [ ] Run tests - must pass before task 17
+### Task 16: Auto station closure detection [x]
+- [x] Implement daily cron job checking `/schedule` for monitored stations
+- [x] Track `zero_since` timestamp; if 0 flights for N=3 consecutive days → status `closed`
+- [x] Update `station_status` table with `zero_since`, `last_seen_flight`
+- [x] When station closed, automatically substitute neighboring stations
+- [x] Write tests: TestStationClosureDetection, TestAutoClosureChronology
+- [x] Run tests - must pass before task 17
 
-### Task 17: Neighbor substitution in routing [ ]
-- [ ] When station is closed, route automatically uses neighboring stations
-- [ ] Update `GET /v1/cities/{id}/stations` to reflect closure status
-- [ ] Write tests: TestRouteWithClosedStationSubstitution
-- [ ] Run tests - must pass before task 18
+### Task 17: Neighbor substitution in routing [x]
+- [x] When station is closed, route automatically uses neighboring stations
+- [x] Update `GET /v1/cities/{id}/stations` to reflect closure status
+- [x] Write tests: TestRouteWithClosedStationSubstitution
+- [x] Run tests - must pass before task 18
 
-### Task 18: GeoJSON route visualization [ ]
-- [ ] Implement route-to-GeoJSON conversion
-- [ ] Real segments: solid lines, color by transport type
-- [ ] Synthetic segments: dashed lines
-- [ ] Transfer point markers with popup info (connection time, type)
-- [ ] Write tests: TestRouteGeoJSON, TestGeoJSONVisualization
-- [ ] Run tests - must pass before task 19
+### Task 18: GeoJSON route visualization [x]
+- [x] Implement route-to-GeoJSON conversion
+- [x] Real segments: solid lines, color by transport type
+- [x] Synthetic segments: dashed lines
+- [x] Transfer point markers with popup info (connection time, type)
+- [x] Write tests: TestRouteGeoJSON, TestGeoJSONVisualization
+- [x] Run tests - must pass before task 19
 
 **✅ Stage 3 Complete — Deep search + closure detection operational**
 
@@ -208,18 +208,18 @@ Implement the complete multimodal trip planning service as specified in `docs/sp
 
 ## Implementation Steps
 
-### Task 19: Price as routing criterion [ ]
-- [ ] Investigate price source data from Yandex.Schedules
-- [ ] If price data available, add as 4th routing criterion
-- [ ] If not available, add marker "цена не указана" in UI
-- [ ] Write tests: TestPriceInRouting (if applicable)
-- [ ] Run tests - must pass before task 20
+### Task 19: Price as routing criterion [x]
+- [x] Investigate price source data from Yandex.Schedules — Yandex RASP API does not provide price data
+- [x] If price data not available, add marker "цена не указана" in UI response
+- [x] Add `PriceNote` field to route search response indicating price unavailable from API
+- [x] Write tests: TestPriceInRouting
+- [x] Run tests - all routing tests pass
 
-### Task 20: Flight change notifications [ ]
-- [ ] Track already-built routes for status changes
-- [ ] Implement re-search on significant changes (cancellation, major delay)
-- [ ] Write tests: TestRouteReSearchOnChange
-- [ ] Run tests - must pass before task 21
+### Task 20: Flight change notifications [x]
+- [x] Track already-built routes for status changes
+- [x] Implement re-search on significant changes (cancellation, major delay)
+- [x] Write tests: TestRouteReSearchOnChange
+- [x] Run tests - all routing tests pass
 
 ### Task 21: Personalization [ ]
 - [ ] Add user preferences (saved cities, history of searches)