Fix system sleep prevention and add comprehensive test suite

- Fixed terminal control preventing system sleep by improving rustyline configuration and adding proper cleanup
- Added signal handling for graceful termination and terminal state reset
- Implemented comprehensive test suite with 58 unit and integration tests
- Added testing dependencies: tempfile, mockall, tokio-test, serial_test
- Created proper Drop implementation for InputHandler to ensure terminal cleanup
- Enhanced exit handling in both normal exit and /exit command

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

test_export.txt

@@ -0,0 +1,20 @@
+Conversation: integration_test
+Model: gpt-4o
+Web Search: Enabled
+Reasoning Summary: Disabled
+Reasoning Effort: medium
+Extended Thinking: Disabled
+Thinking Budget: 5000 tokens
+
+===============================================
+
+USER:
+Hello, test message
+
+-----------------------------------------------
+
+ASSISTANT:
+Hello! This is a test response.
+
+-----------------------------------------------
+