Skip notifications for upcoming/premiere videos

Videos that haven't premiered yet were triggering repeated notifications
on every background refresh cycle. Filter them out by checking isUpcoming
flag and rejecting videos with future publish dates.

Also decode isUpcoming/premiereTimestamp from Yattee Server feed responses
instead of hardcoding false/nil.

Yattee/Services/API/YatteeServerAPI.swift

@@ -402,6 +402,8 @@ struct ServerFeedVideo: Decodable, Sendable {
     let videoThumbnails: [YatteeThumbnail]?
     let extractor: String
     let videoUrl: String?
+    let isUpcoming: Bool?
+    let premiereTimestamp: Int64?
 
     func toVideo() -> Video? {
         // Determine content source based on extractor
@@ -427,8 +429,8 @@ struct ServerFeedVideo: Decodable, Sendable {
             likeCount: nil,
             thumbnails: videoThumbnails?.map { $0.toThumbnail() } ?? [],
             isLive: false,
-            isUpcoming: false,
-            scheduledStartTime: nil
+            isUpcoming: isUpcoming ?? false,
+            scheduledStartTime: premiereTimestamp.map { Date(timeIntervalSince1970: TimeInterval($0)) }
         )
     }
 }