feat: Mark All as Read — bulk action with optimistic UI and rollback

APIClient:
- markAllRead(storyIds💊) — POST /me/read/bulk with device ID, timestamp,
  source label, and pill name so backend can record context

Models:
- PaginatedStories gains unreadCount, readSuppressedCount, lastReadSyncAt,
  activePill — backend now returns these so the UI can report honest state

SignalFeedView:
- Header "…" menu replaces the standalone settings button; menu contains
  "Mark all as read" (disabled while pending or when nothing is unread) and
  a Settings item
- markAllRead() captures all visible unread IDs, optimistically inserts
  ReadStory for each, shows toast ("Marked N stories as read"), then fires
  the bulk API; on failure deletes the optimistic ReadStory records and
  shows an honest error toast ("Sync failed. Stories may reappear until retry.")
- Toast auto-dismisses after 3.5s, appears at the bottom of the ZStack
  with a slide-up + opacity animation

Cross-pill suppression was already in place — backend applies
unread_story_condition() to every /stories request regardless of tags,
so stories marked read in All disappear from Tech, Sport, etc. on the
next pill fetch.

Co-Authored-By: Kutesir <tqwyy79vzn@privaterelay.appleid.com>

Jarvis/Networking/APIClient.swift

@@ -111,6 +111,16 @@ actor APIClient {
         try await delete("/stories/\(id)/read")
     }
 
+    func markAllRead(storyIds: [String], pill: String) async throws {
+        try await postVoid("/me/read/bulk", body: [
+            "storyIds": storyIds,
+            "readAt": ISO8601DateFormatter().string(from: Date()),
+            "source": "mark_all_as_read",
+            "pill": pill,
+            "deviceId": deviceId,
+        ])
+    }
+
     // MARK: - Articles
 
     func fetchArticle(id: String) async throws -> Article {