更新方形Logo和头颈部CT默认分类

- 侧边栏 Logo 改为导入根目录 logo_square.png，favicon 也切换为 /logo_square.png，并让前端服务显式提供该根目录图片。

- 头颈部CT分割默认模板分类名改为纯中文，去掉括号英文翻译，颜色和 maskid 保持用户给定顺序。

- 增加旧版头颈部CT英文括号 label 的窄迁移，启动 seed 时自动把旧默认系统模板更新为纯中文默认。

- 更新前端 Logo 测试、后端默认模板和恢复出厂设置测试，覆盖纯中文分类和根目录方形 Logo。

- 更新 AGENTS、README、前端审计、需求冻结和测试计划文档，记录根目录 Logo 和头颈部CT纯中文默认分类。

backend/services/default_templates.py

@@ -86,16 +86,16 @@ def bundled_default_template_definitions() -> list[dict]:
             "classes": _with_reserved_unclassified_class(_template_classes(
                 "头颈部CT分割",
                 [
-                    "肿瘤/结节 (Tumor/Nodule)",
-                    "下颌骨 (Mandible)",
-                    "甲状腺 (Thyroid)",
-                    "气管 (Trachea)",
-                    "颈椎 (Cervical Spine)",
-                    "颈动脉 (Carotid Artery)",
-                    "颈静脉 (Jugular Vein)",
-                    "腮腺 (Parotid Gland)",
-                    "下颌下腺 (Submandibular Gland)",
-                    "舌骨 (Hyoid Bone)",
+                    "肿瘤/结节",
+                    "下颌骨",
+                    "甲状腺",
+                    "气管",
+                    "颈椎",
+                    "颈动脉",
+                    "颈静脉",
+                    "腮腺",
+                    "下颌下腺",
+                    "舌骨",
                 ],
                 [
                     (255, 0, 0),
@@ -115,6 +115,19 @@ def bundled_default_template_definitions() -> list[dict]:
     ]
 
 
+def _has_legacy_head_neck_english_labels(template: Template) -> bool:
+    if template.name != "头颈部CT分割":
+        return False
+    classes = (template.mapping_rules or {}).get("classes") or []
+    return any(
+        isinstance(item, dict)
+        and isinstance(item.get("name"), str)
+        and "(" in item["name"]
+        and ")" in item["name"]
+        for item in classes
+    )
+
+
 def ensure_default_templates(db: Session, *, restore_existing: bool = False) -> list[Template]:
     """Create bundled system templates, optionally restoring existing ones exactly."""
     templates: list[Template] = []
@@ -126,7 +139,7 @@ def ensure_default_templates(db: Session, *, restore_existing: bool = False) ->
         if existing is None:
             existing = Template(owner_user_id=None)
             db.add(existing)
-        elif not restore_existing:
+        elif not restore_existing and not _has_legacy_head_neck_english_labels(existing):
             templates.append(existing)
             continue