fix: API key limit now only counts active keys and uses config value

- Modified API key limit to count only active (non-deleted) keys instead of all keys
- Fixed frontend to use MAX_API_KEYS_PER_USER environment variable instead of hardcoded value
- Added activeApiKeysCount computed property to filter deleted keys
- Updated user profile endpoint to include maxApiKeysPerUser config
- Enhanced user store to persist and retrieve config values

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

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

src/routes/userRoutes.js

@@ -116,6 +116,9 @@ router.get('/profile', authenticateUser, async (req, res) => {
         lastLoginAt: user.lastLoginAt,
         apiKeyCount: user.apiKeyCount,
         totalUsage: user.totalUsage
+      },
+      config: {
+        maxApiKeysPerUser: config.userManagement.maxApiKeysPerUser
       }
     })
   } catch (error) {