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>

src/cli.rs

@@ -78,7 +78,7 @@ impl ChatCLI {
         }
 
         self.session.save()?;
-        self.input.save_history()?;
+        self.input.cleanup()?; // Use cleanup instead of just save_history
         Ok(())
     }
 
@@ -187,6 +187,7 @@ impl ChatCLI {
             }
             "/exit" => {
                 self.session.save()?;
+                self.input.cleanup()?; // Clean up terminal state
                 self.display.print_info("Session saved. Goodbye!");
                 return Ok(false);
             }