feat: Limit config backups to 3 most recent files

Modified the backupConfigFile function to automatically clean up old backups,
keeping only the 3 most recent backup files. This prevents the config directory
from accumulating excessive backup files over time.

The implementation:
- Creates timestamped backups as before
- After each new backup, scans for existing backups
- Sorts backups by timestamp (newest first)
- Deletes all but the 3 most recent backups
- Gracefully handles cleanup errors with warnings

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

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

src/utils/index.ts

@@ -1,6 +1,7 @@
 import fs from "node:fs/promises";
 import readline from "node:readline";
 import JSON5 from "json5";
+import path from "node:path";
 import {
   CONFIG_FILE,
   DEFAULT_CONFIG,
@@ -91,6 +92,30 @@ export const backupConfigFile = async () => {
       const timestamp = new Date().toISOString().replace(/[:.]/g, '-');
       const backupPath = `${CONFIG_FILE}.${timestamp}.bak`;
       await fs.copyFile(CONFIG_FILE, backupPath);
+      
+      // Clean up old backups, keeping only the 3 most recent
+      try {
+        const configDir = path.dirname(CONFIG_FILE);
+        const configFileName = path.basename(CONFIG_FILE);
+        const files = await fs.readdir(configDir);
+        
+        // Find all backup files for this config
+        const backupFiles = files
+          .filter(file => file.startsWith(configFileName) && file.endsWith('.bak'))
+          .sort()
+          .reverse(); // Sort in descending order (newest first)
+        
+        // Delete all but the 3 most recent backups
+        if (backupFiles.length > 3) {
+          for (let i = 3; i < backupFiles.length; i++) {
+            const oldBackupPath = path.join(configDir, backupFiles[i]);
+            await fs.unlink(oldBackupPath);
+          }
+        }
+      } catch (cleanupError) {
+        console.warn("Failed to clean up old backups:", cleanupError);
+      }
+      
       return backupPath;
     }
   } catch (error) {