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/Models/Models.swift

@@ -136,6 +136,10 @@ struct PaginatedStories: Codable {
     let nextCursor: String?
     let hasMore: Bool
     let total: Int
+    let unreadCount: Int?
+    let readSuppressedCount: Int?
+    let lastReadSyncAt: Date?
+    let activePill: String?
 }
 
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