feat: add run_cmd_fatal, fix Fedora, improve CI (#1369)

## Summary

This PR contains three related improvements:

### 1. Add `run_cmd_fatal` for critical operations
- New helper function that wraps `run_cmd` and exits on failure
- Converts critical operations (package installs, PKI setup, certificate
generation) to fail fast
- Non-critical operations (systemctl, cleanup) still use `run_cmd`
- Password-protected client certs run directly to preserve interactive
prompt

### 2. Fix Fedora installation
- Skip Copr repository setup since Fedora already ships OpenVPN 2.6.x
- Simplifies installation and removes external repository dependency

### 3. Improve CI test reliability
- Fail fast when `openvpn-test.service` fails during startup
- Add `journalctl` output to error diagnostics
- Display service status in wait loop
- Increase VPN gateway ping count from 3 to 10 for stability

test/client-entrypoint.sh

@@ -74,7 +74,7 @@ fi
 
 # Test 2: Ping VPN gateway
 echo "Test 2: Pinging VPN gateway (10.8.0.1)..."
-if ping -c 3 10.8.0.1; then
+if ping -c 10 10.8.0.1; then
 	echo "PASS: Can ping VPN gateway"
 else
 	echo "FAIL: Cannot ping VPN gateway"