Refactor data sources and feed model

IrisCompanion/iris/DataSources/POIDataSource.swift

@@ -15,13 +15,18 @@ struct POIDataSourceConfig: Sendable {
 
 /// Placeholder POI source. Hook point for MapKit / local cache / server-driven POIs.
 final class POIDataSource {
+    struct POI: Sendable, Equatable {
+        let id: String
+        let name: String
+    }
+
     private let config: POIDataSourceConfig
 
     init(config: POIDataSourceConfig = .init()) {
         self.config = config
     }
 
-    func candidates(for location: CLLocation, now: Int) async throws -> [Candidate] {
+    func data(for location: CLLocation, now: Int) async throws -> [POI] {
         // Phase 1 stub: return nothing.
         // (Still async/throws so the orchestrator can treat it uniformly with real implementations later.)
         _ = config
@@ -30,4 +35,3 @@ final class POIDataSource {
         return []
     }
 }
-