integration: add run ID isolation for concurrent test execution

Add run ID-based isolation to container naming and network setup to
enable multiple integration tests to run concurrently on the same
Docker daemon without conflicts.

Changes:
- hsic: Add run ID prefix to headscale container names and use dynamic
  port allocation for metrics endpoint (port 0 lets kernel assign)
- tsic: Add run ID prefix to tailscale container names
- dsic: Add run ID prefix to DERP container names
- scenario: Use run ID-aware test suite container name for network setup

Container naming now follows: {type}-{runIDShort}-{identifier}-{hash}
Example: ts-mdjtzx-1-74-fgdyls, hs-mdjtzx-pingallbyip-abc123

The run ID is obtained from HEADSCALE_INTEGRATION_RUN_ID environment
variable via dockertestutil.GetIntegrationRunID().

integration/dsic/dsic.go

@@ -147,7 +147,18 @@ func New(
 		return nil, err
 	}
 
-	hostname := fmt.Sprintf("derp-%s-%s", strings.ReplaceAll(version, ".", "-"), hash)
+	// Include run ID in hostname for easier identification of which test run owns this container
+	runID := dockertestutil.GetIntegrationRunID()
+
+	var hostname string
+
+	if runID != "" {
+		// Use last 6 chars of run ID (the random hash part) for brevity
+		runIDShort := runID[len(runID)-6:]
+		hostname = fmt.Sprintf("derp-%s-%s-%s", runIDShort, strings.ReplaceAll(version, ".", "-"), hash)
+	} else {
+		hostname = fmt.Sprintf("derp-%s-%s", strings.ReplaceAll(version, ".", "-"), hash)
+	}
 	tlsCert, tlsKey, err := integrationutil.CreateCertificate(hostname)
 	if err != nil {
 		return nil, fmt.Errorf("failed to create certificates for headscale test: %w", err)