feat(bg): add background feed refresh every ~30 min

Registers com.kisani.jarvis.feed.refresh as a BGAppRefreshTask.
On each fire it fetches the latest 40 stories and upserts CachedStory
rows so the SwiftData cache is warm before the user opens the app.
Already-cached rows have signalScore / sourceCount refreshed in-place.

Single ModelContainer owned by JarvisApp and shared via
BackgroundRefreshManager.container to avoid multi-container conflicts.
BG task ID registered in AppDelegate and declared in project.yml.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Jarvis/Store/BackgroundRefreshManager.swift

@@ -0,0 +1,77 @@
+// BackgroundRefreshManager.swift
+// Jarvis — background story cache refresh. Fires via BGAppRefreshTask every ~30 min,
+// fetches the latest feed, and upserts CachedStory rows so the SwiftData cache is
+// warm before the user opens the app.
+
+import Foundation
+import BackgroundTasks
+import SwiftData
+
+let jarvisFeedRefreshID = "com.kisani.jarvis.feed.refresh"
+
+enum BackgroundRefreshManager {
+
+    // Injected once from JarvisApp so the BG task can open a context on the same store.
+    static var container: ModelContainer?
+
+    // MARK: - Task handler
+
+    static func handleFeedRefresh(task: BGAppRefreshTask) {
+        // Reschedule first — if the task is killed we still get another run later.
+        scheduleFeedRefresh()
+
+        guard let container else {
+            task.setTaskCompleted(success: false)
+            return
+        }
+
+        let work = Task {
+            await fetchAndCache(container: container)
+        }
+
+        task.expirationHandler = {
+            work.cancel()
+            task.setTaskCompleted(success: false)
+        }
+
+        Task {
+            _ = await work.result
+            task.setTaskCompleted(success: !work.isCancelled)
+        }
+    }
+
+    // MARK: - Core fetch + upsert
+
+    private static func fetchAndCache(container: ModelContainer) async {
+        do {
+            let page = try await APIClient.shared.fetchStories(limit: 40)
+            let context = ModelContext(container)
+
+            for story in page.data {
+                let id = story.id
+                if let existing = (try? context.fetch(
+                    FetchDescriptor<CachedStory>(predicate: #Predicate { $0.id == id })))?.first {
+                    // Refresh signal score and freshness on already-cached rows.
+                    existing.signalScore = story.signalScore
+                    existing.sourceCount = story.sourceCount
+                    existing.updatedAt   = story.updatedAt
+                } else {
+                    context.insert(CachedStory(from: story))
+                }
+            }
+
+            try? context.save()
+        } catch {
+            // Network unavailable in background — fail silently, next run will catch up.
+        }
+    }
+
+    // MARK: - Schedule
+
+    static func scheduleFeedRefresh() {
+        let req = BGAppRefreshTaskRequest(identifier: jarvisFeedRefreshID)
+        // iOS enforces a minimum interval (~15 min); 30 min is a reasonable target.
+        req.earliestBeginDate = Date(timeIntervalSinceNow: 30 * 60)
+        try? BGTaskScheduler.shared.submit(req)
+    }
+}