feat: massive overhaul to manage costs (#103)

### Explanation

_No response_

### Issue

Closes #102

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- [ ] My contribution complies with the [Contributor Covenant](https://docs.nhcarrigan.com/dev/covenant/).

### Dependencies

- [ ] I have pinned the dependencies to a specific patch version.

### Style

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### Tests

- [ ] My contribution adds new code, and I have added tests to cover it.
- [ ] My contribution modifies existing code, and I have updated the tests to reflect these changes.
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Reviewed-on: #103
Co-authored-by: Naomi Carrigan <commits@nhcarrigan.com>
Co-committed-by: Naomi Carrigan <commits@nhcarrigan.com>

src/lib/notifications/notificationManager.ts

@@ -90,6 +90,8 @@ class NotificationManager {
         return "Successfully connected to Claude Code";
       case NotificationType.TASK_START:
         return "Starting task...";
+      case NotificationType.COST_ALERT:
+        return "You've exceeded your cost threshold!";
       default:
         return "Notification";
     }
@@ -115,6 +117,10 @@ class NotificationManager {
   async notifyTaskStart(message?: string): Promise<void> {
     await this.notify(NotificationType.TASK_START, message);
   }
+
+  async notifyCostAlert(message?: string): Promise<void> {
+    await this.notify(NotificationType.COST_ALERT, message);
+  }
 }
 
 // Export singleton instance