Add EV charging discovery feature (disabled by flag)

- Create EVChargingService using MapKit POI search for EV chargers
- Add ItineraryBuilder.enrichWithEVChargers() for post-planning enrichment
- Update TravelSection in TripDetailView with expandable charger list
- Add FeatureFlags.enableEVCharging toggle (default: false)
- Include EVChargingFeature.md documenting API overhead

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

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

SportsTime/Core/FeatureFlags.swift

@@ -0,0 +1,14 @@
+//
+//  FeatureFlags.swift
+//  SportsTime
+//
+//  Feature toggles for enabling/disabling features during development.
+//
+
+import Foundation
+
+enum FeatureFlags {
+    /// Enable EV charging station discovery along routes.
+    /// When enabled, trip planning will search for EV chargers using MapKit.
+    static let enableEVCharging = false
+}