ICMP Ping Monitor fails with "ping: executable file not found in $PATH" error in monolithic Docker deployment

**Summary**

The ICMP Ping monitoring feature is failing intermittently due to the ping executable not being available in the Docker container's $PATH. This causes monitors to alternate between "Up" and "Down" states.

**Environment**

- Peekaping Version: v0.0.44
- Deployment Method: Docker (Monolithic mode)
- Monitor Type: ICMP Ping

**Expected Behavior**

ICMP Ping monitors should consistently check host reachability and report accurate status without dependency errors.

**Actual Behavior**

Ping monitors fail intermittently with the following error:

`
Ping failed: ping command failed: exec: "ping": executable file not found in $PATH`

The monitor status fluctuates:

- ✅ 07:40:00 AM: Ping successful, RTT: 3.419854ms
- ❌ 07:39:41 AM: Ping failed with the error above

**Steps to Reproduce**

- Deploy Peekaping using the official monolithic Docker image with PostgreSQL
- Create a new monitor with type "Ping (ICMP)"
- Configure it to monitor any DNS server or IP address
- Observe the monitor status over time
- Error appears intermittently in notifications

**Screenshots**

Look at the Dockerfile for the monolithic deployment to see if the `iputils-ping` package is installed. Check the Go code that executes the ping command, likely in a monitor execution or ICMP service file. Verify the container's PATH and test that the ping binary is present and executable. A successful fix will have the ping command run reliably from within the Docker container.

Rédigé par le modèle d'indexation à partir du texte de l'issue.