feat: 添加测试框架及功能测试用例

test: 实现BDD测试框架及功能测试
docs: 添加测试配置文件及文档
refactor: 重构命令处理逻辑以支持测试

tests/features/commands/shell.feature

@@ -0,0 +1,22 @@
+Feature: /shell command — run host shell commands
+
+  Background:
+    Given user "user_abc123" is sending commands
+
+  Scenario: No arguments shows usage
+    When user sends "/shell"
+    Then reply contains "Usage: /shell"
+
+  Scenario: Runs echo and returns output
+    When user sends "/shell echo hello"
+    Then reply contains "hello"
+    And reply contains "exit code: 0"
+
+  Scenario: Blocked dangerous command is rejected
+    When user sends "/shell rm -rf /"
+    Then reply contains "Blocked"
+    And reply does not contain "exit code"
+
+  Scenario: Non-zero exit code is reported
+    When user sends "/shell exit 1"
+    Then reply contains "exit code"