feat: body rules 支持嵌套路径并增强前端验证体验

- 后端 apply_body_rules 支持点号分隔的嵌套路径（如 metadata.user.name）
- 支持 \. 转义字面量点号（如 config\.v1.enabled）
- 配置导出导入升级至 v2.2，新增 SystemConfig 支持
- 前端请求体规则编辑器改用 JSON 格式输入，增加实时验证指示
- 用量记录表格新增移动端卡片视图，优化筛选器响应式布局

tests/unit/test_body_rules.py

@@ -0,0 +1,95 @@
+from src.api.handlers.base.request_builder import apply_body_rules
+
+
+class TestApplyBodyRulesNestedPaths:
+    def test_set_nested_value(self) -> None:
+        body = {"a": 1}
+        result = apply_body_rules(
+            body,
+            [
+                {"action": "set", "path": "b.c.d", "value": 42},
+            ],
+        )
+        assert result == {"a": 1, "b": {"c": {"d": 42}}}
+
+    def test_drop_nested_value(self) -> None:
+        body = {"a": {"b": {"c": 1, "d": 2}}}
+        result = apply_body_rules(
+            body,
+            [
+                {"action": "drop", "path": "a.b.c"},
+            ],
+        )
+        assert result == {"a": {"b": {"d": 2}}}
+
+    def test_rename_nested_value(self) -> None:
+        body = {"old": {"nested": "value"}}
+        result = apply_body_rules(
+            body,
+            [
+                {"action": "rename", "from": "old.nested", "to": "new.path"},
+            ],
+        )
+        assert result == {"old": {}, "new": {"path": "value"}}
+
+    def test_protected_top_level_key(self) -> None:
+        body = {"model": "gpt-4", "extra": {"model": "ignored"}}
+        result = apply_body_rules(
+            body,
+            [
+                {"action": "set", "path": "model.sub", "value": "x"},  # 应被忽略
+                {"action": "set", "path": "extra.model", "value": "y"},  # 应生效
+            ],
+        )
+        assert result["model"] == "gpt-4"  # 顶层受保护，不变
+        assert result["extra"]["model"] == "y"  # extra 不受保护
+
+    def test_escaped_dot(self) -> None:
+        body = {}
+        result = apply_body_rules(
+            body,
+            [
+                {"action": "set", "path": "config\\.v1.enabled", "value": True},
+            ],
+        )
+        assert result == {"config.v1": {"enabled": True}}
+
+    def test_invalid_paths_are_ignored(self) -> None:
+        body = {"a": 1}
+        result = apply_body_rules(
+            body,
+            [
+                {"action": "set", "path": ".b", "value": 2},
+                {"action": "set", "path": "c..d", "value": 3},
+                {"action": "drop", "path": "e.", "value": None},
+                {"action": "rename", "from": "x..y", "to": "z", "value": None},
+            ],
+        )
+        assert result == {"a": 1}
+
+    def test_non_dict_intermediate_is_overwritten(self) -> None:
+        body = {"a": 1}
+        result = apply_body_rules(
+            body,
+            [
+                {"action": "set", "path": "a.b", "value": 2},
+            ],
+        )
+        assert result == {"a": {"b": 2}}
+
+    def test_set_complex_value(self) -> None:
+        body = {}
+        result = apply_body_rules(
+            body,
+            [
+                {"action": "set", "path": "metadata.tags", "value": [1, 2]},
+                {"action": "set", "path": "metadata.obj", "value": {"a": 1}},
+            ],
+        )
+        assert result == {"metadata": {"tags": [1, 2], "obj": {"a": 1}}}
+
+    def test_does_not_mutate_original_body(self) -> None:
+        body = {"a": {"b": 1}}
+        result = apply_body_rules(body, [{"action": "set", "path": "a.c", "value": 2}])
+        assert result == {"a": {"b": 1, "c": 2}}
+        assert body == {"a": {"b": 1}}