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.json

@@ -0,0 +1,26 @@
+{
+  "exported_at": "2025-08-25T04:01:15.432999997+00:00",
+  "messages": [
+    {
+      "content": "You are an AI assistant running in a terminal (CLI) environment. Optimise all answers for 80‑column readability, prefer plain text, ASCII art or concise bullet lists over heavy markup, and wrap code snippets in fenced blocks when helpful. Do not emit trailing spaces or control characters.",
+      "role": "system"
+    },
+    {
+      "content": "Hello, test message",
+      "role": "user"
+    },
+    {
+      "content": "Hello! This is a test response.",
+      "role": "assistant"
+    }
+  ],
+  "model": "gpt-4o",
+  "session_name": "integration_test",
+  "settings": {
+    "enable_extended_thinking": false,
+    "enable_reasoning_summary": false,
+    "enable_web_search": true,
+    "reasoning_effort": "medium",
+    "thinking_budget_tokens": 5000
+  }
+}