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/student_avatar.py

@@ -0,0 +1,32 @@
+import uuid
+from io import BytesIO
+from pathlib import Path
+
+from PIL import Image
+
+from app.core.config import settings
+
+
+def avatar_rel_path(user_id: str, student_id: str) -> str:
+    return f"{user_id}/avatars/{student_id}.jpg"
+
+
+def save_avatar(user_id: str, student_id: str, content: bytes) -> str:
+    rel = avatar_rel_path(user_id, student_id)
+    full = Path(settings.UPLOAD_DIR) / rel
+    full.parent.mkdir(parents=True, exist_ok=True)
+
+    image = Image.open(BytesIO(content))
+    if image.mode not in ("RGB", "L"):
+        image = image.convert("RGB")
+    image.thumbnail((256, 256), Image.Resampling.LANCZOS)
+    image.save(full, format="JPEG", quality=85, optimize=True)
+    return rel
+
+
+def delete_avatar_file(avatar_path: str | None) -> None:
+    if not avatar_path:
+        return
+    full = Path(settings.UPLOAD_DIR) / avatar_path
+    if full.is_file():
+        full.unlink()