学生资料设置、头像与自动备份恢复。

首页卡片支持修改/删除；详情页设置 Tab 可维护学校、年级与头像；系统设置新增数据备份下载与恢复；备份默认存 /root/grade-archive-backups，详见 docs/BACKUP.md。

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/app/services/migrate.py

@@ -101,3 +101,14 @@ def run_migrations() -> None:
                         "ALTER TABLE system_settings ADD COLUMN ai_review_enabled BOOLEAN NOT NULL DEFAULT TRUE"
                     )
                 )
+
+    student_columns = {col["name"] for col in inspector.get_columns("students")}
+    student_alters: list[str] = []
+    if "school_name" not in student_columns:
+        student_alters.append("ADD COLUMN school_name VARCHAR(128)")
+    if "avatar_path" not in student_columns:
+        student_alters.append("ADD COLUMN avatar_path VARCHAR(512)")
+    if student_alters:
+        with engine.begin() as conn:
+            for clause in student_alters:
+                conn.execute(text(f"ALTER TABLE students {clause}"))