Feat: notify on empty tactical class slot

module/config/i18n/en-US.json

@@ -1561,6 +1561,10 @@
     "MinLevel": {
       "name": "Add Students with Level >= X Only",
       "help": ""
+    },
+    "EnableNotify": {
+      "name": "Notify on Empty Slot",
+      "help": "Send a notification when there is an empty slot in the Tactical Academy: a ship girl has finished studying and 'Level Skills' is disabled, or enabled but failed to assign a new student"
     }
   },
   "Research": {

module/config/i18n/ja-JP.json

@@ -1561,6 +1561,10 @@
     "MinLevel": {
       "name": "レベルがX以上のキャラクターのみを追加してください。",
       "help": ""
+    },
+    "EnableNotify": {
+      "name": "空席通知を送信",
+      "help": "戦術学院に空席がある時に通知を送信：艦娘が学習を完了し、かつ'新しいスキルを学ぶ'が無効、または有効だが新規生徒の割り当てに失敗した時"
     }
   },
   "Research": {

module/config/i18n/zh-CN.json

@@ -1561,6 +1561,10 @@
     "MinLevel": {
       "name": "仅添加等级 >= X 的角色",
       "help": ""
+    },
+    "EnableNotify": {
+      "name": "推送空位提醒",
+      "help": "在战术学院有空位时推送通知：舰娘完成学习且未启用'学习新技能'，或启用了但指派失败时"
     }
   },
   "Research": {

module/config/i18n/zh-TW.json

@@ -1561,6 +1561,10 @@
     "MinLevel": {
       "name": "僅新增等級 >= X 的角色",
       "help": ""
+    },
+    "EnableNotify": {
+      "name": "推送空位提醒",
+      "help": "在戰術學院有空位時推送通知：艦娘完成學習且未啟用'學習新技能'，或啟用了但指派失敗時"
     }
   },
   "Research": {