Add Yahoo Finance stock data integration

- Add StockDataSource to fetch quotes from Yahoo Finance API
- Add StockSettingsStore for persisting user's stock symbols
- Add StockSettingsView with UI to manage symbols (max 5)
- Add STOCK feed item type and ranker weight (0.3)
- Integrate stock fetch into ContextOrchestrator pipeline
- Stock cards appear in FYI bucket and sync to Glass via BLE

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

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

IrisCompanion/iris/Models/Winner.swift

@@ -16,5 +16,6 @@ enum FeedItemType: String, Codable, CaseIterable {
     case nowPlaying = "NOW_PLAYING"
     case currentWeather = "CURRENT_WEATHER"
     case calendarEvent = "CALENDAR_EVENT"
+    case stock = "STOCK"
     case allQuiet = "ALL_QUIET"
 }