Feature request: Push endpoint should honor status parameter to change monitor state

**Description:**
First of all — great work on Peekaping! I really like the UI and overall usability.
While testing the Push monitor, I noticed that the `status` and `msg` query parameters are accepted but not applied to the monitor’s state.

- The `msg` value appears in the logs.
- The `status` value (`up`, `down`, `start`) seems to be ignored.
- The check remains green as long as pings arrive within the allowed interval.

Is this the intended behavior or something still in progress?

**Expected behavior:**
Sending:
```bash
curl "https://demo.peekaping.com/api/v1/push/?status=down&msg=Manual fail"
```
should immediately mark the monitor as failed, while
```bash
curl "https://demo.peekaping.com/api/v1/push/?status=up&msg=OK"
```
should mark it as healthy again.

**Actual behavior:**
The API always returns a success response but does not modify the check state.

**API response:**
```json
{
"ok": "true"
}
```
This response is returned regardless of the `status` value. The monitor remains green until no further pings arrive and the interval times out.

**Steps to reproduce:**
1. Create a Push monitor.
2. Send one `status=up` request.
3. Send `status=down` — returns `"ok": "true"`, but the check state does not change.

**Suggestion:**
Evaluate the `status` parameter to allow explicit state changes (`up` → healthy, `down` → failed, `start` → pending).
This would make the Push endpoint compatible with heartbeat-based tools such as Healthchecks.io.

Find the push endpoint handler in the API routes, likely in a file like `api/v1/push.go`. Examine how it processes the `status` and `msg` query parameters. The logic to update a monitor's state based on the `status` parameter needs to be added. Look for existing monitor state management functions to understand the data model. Test by creating a push monitor and sending curl requests to verify the state changes.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.