feat: 添加账号支持选择学习平台

账号新增 platform 字段，登录/刷新课程/发现课程按平台分发；同时把 JS 脚本收进 script/（目录规范调整）。

src/study_tool/models.py

@@ -7,6 +7,7 @@ class LoginIn(BaseModel):
     username: str = ""
     password: str = ""
     account_id: str = ""        # 只给账号 id 时，用户名/密码从 SQLite 里取，密码不出库
+    platform: str = "guanyixue"   # 没传 account_id 时按它选平台
 
 
 class AccountsIn(BaseModel):
@@ -16,6 +17,7 @@ class AccountsIn(BaseModel):
 class AccountIn(BaseModel):
     id: str = ""
     username: str = ""
+    platform: str = "guanyixue"   # 添加账号时选的平台
     password: str | None = None      # 不传 = 保留库里已有的密码
     note: str = ""
     user: str = ""
@@ -33,6 +35,7 @@ class AccountIn(BaseModel):
 
 class CookiesIn(BaseModel):
     cookies: list
+    platform: str = "guanyixue"
 
 
 class DiscoverIn(BaseModel):
@@ -40,6 +43,7 @@ class DiscoverIn(BaseModel):
     plan_id: str
     project_id: str
     name: str = ""
+    platform: str = "guanyixue"
 
 
 class StudyIn(BaseModel):
@@ -72,6 +76,7 @@ class QuizIn(BaseModel):
     plan_id: str = ""
     project_id: str = ""
     name: str = ""
+    platform: str = "guanyixue"
     # retake=True：交卷后点「再考一次」，让平台生成新答卷（消耗一次机会）
     retake: bool = False
     period_id: str = ""         # 指定要重考/查看的课时（不传就按原逻辑挑第一个）