Add TFL train disruption alerts integration

Query TFL API for Tube and Elizabeth Line status, displaying
disruptions as feed cards. Major disruptions (severity 1-6) appear
as RIGHT_NOW spotlight cards, minor delays (7-9) as FYI items.

- Add TFLDataSource with 2-min cache and severity classification
- Add .transitAlert FeedItemType with 0.85 base weight
- Wire up async fetch in ContextOrchestrator pipeline
- Handle timeout and failure cases gracefully

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

IrisCompanion/iris/Models/HeuristicRanker.swift

@@ -86,6 +86,7 @@ final class HeuristicRanker {
         switch type {
         case .weatherWarning: return 1.0
         case .weatherAlert: return 0.9
+        case .transitAlert: return 0.85
         case .calendarEvent: return 0.8
         case .transit: return 0.75
         case .poiNearby: return 0.6

IrisCompanion/iris/Models/Winner.swift

@@ -17,5 +17,6 @@ enum FeedItemType: String, Codable, CaseIterable {
     case currentWeather = "CURRENT_WEATHER"
     case calendarEvent = "CALENDAR_EVENT"
     case stock = "STOCK"
+    case transitAlert = "TRANSIT_ALERT"
     case allQuiet = "ALL_QUIET"
 }