feat: Per-user story seen-receipt exclusions

feat: Story seen button mode (button / toggle)
feat: Long-press menu on the story seen button (mark seen, exclude, settings)
feat: Auto mark-seen on exclude for both stories and DM chats
imp: Cleaner exclusion menu wording across stories and DMs
imp: Tweak settings now update in real time for exclude ui
imp: Ability to batch select in both stories and messages exclude UI

src/Settings/SCISettingsBackup.m

@@ -404,6 +404,7 @@ typedef NS_ENUM(NSInteger, SCIBackupPreviewRowKind) {
 + (NSArray<NSString *> *)extraDataKeys {
     return @[
         @"excluded_threads",
+        @"excluded_story_users",
     ];
 }