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/agent/passthrough.feature

@@ -0,0 +1,19 @@
+Feature: Direct (passthrough) mode — bypass LLM for CC sessions
+
+  Background:
+    Given user "user_abc123" is sending commands
+    And run_claude returns "Done. Here is the result."
+
+  Scenario: Passthrough sends directly to CC without LLM
+    Given user has session "sess01" in "/tmp/proj1"
+    And active session is "sess01"
+    And direct mode is enabled for user "user_abc123"
+    When user sends agent message "run the tests"
+    Then run_claude was called
+    And reply contains "Done. Here is the result."
+
+  Scenario: Passthrough on missing session clears active conv
+    Given active session is "ghost_session_id" which does not exist
+    And direct mode is enabled for user "user_abc123"
+    When user sends agent message "hello"
+    Then active session for user "user_abc123" is None