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

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+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

tests/features/agent/routing.feature

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+Feature: LLM smart routing — agent routes messages to correct tools
+
+  Background:
+    Given user "user_abc123" is in smart mode
+    And run_claude returns "I created the component for you."
+
+  @vcr
+  Scenario: Agent creates new session for project task
+    Given vcr cassette "agent/routing_new_session.yaml"
+    When user sends agent message "create a React app in todo_app folder"
+    Then agent created a session for user "user_abc123"
+    And reply is not empty
+
+  @vcr
+  Scenario: Agent answers general question without creating session
+    Given vcr cassette "agent/routing_general_qa.yaml"
+    When user sends agent message "what is a Python generator?"
+    Then no session is created for user "user_abc123"
+    And reply is not empty
+
+  @vcr
+  Scenario: Agent sends follow-up to existing session
+    Given user has active session "sess01" in "/tmp/proj1"
+    And vcr cassette "agent/routing_follow_up.yaml"
+    When user sends agent message "now add tests for that"
+    Then run_claude was called
+    And reply is not empty
+
+  @vcr
+  Scenario: Agent answers direct QA without tools when no active session
+    Given no active session for user "user_abc123"
+    And vcr cassette "agent/routing_direct_qa.yaml"
+    When user sends agent message "explain async/await in Python"
+    Then reply is not empty
+    And reply does not contain "Max iterations"