fix: use modelContext.container — \.modelContainer is not an Environment key

CI caught this: the sync-lag fix referenced a nonexistent SwiftUI
environment value. The container is reached through the context.

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

Jarvis/Views/Home/SignalFeedView.swift

@@ -10,7 +10,6 @@ struct SignalFeedView: View {
     @EnvironmentObject var ws: WebSocketManager
     @EnvironmentObject var settings: ServerSettings
     @Environment(\.modelContext) private var modelContext
-    @Environment(\.modelContainer) private var modelContainer
 
     @Query private var cachedStories: [CachedStory]
     @Query private var cachedArticles: [CachedArticle]
@@ -724,7 +723,7 @@ struct SignalFeedView: View {
 
     private func cacheStories(_ stories: [StorySummary]) {
         guard !stories.isEmpty else { return }
-        let container = modelContainer
+        let container = modelContext.container
         Task.detached {
             let ctx = ModelContext(container)
             let existing = (try? ctx.fetch(FetchDescriptor<CachedStory>())) ?? []