Fix Docker build context and image tag issues

- Create .dockerignore to exclude unnecessary files (.travis.yml, .git, etc.)
- Remove Tag field from FromDockerfile - testcontainers generates its own tag format
- Fixes 'invalid reference format' error (UUID:TAG:latest) and tar pipe errors

Author: zph

.dockerignore

@@ -0,0 +1,30 @@
+# Exclude unnecessary files from Docker build context
+.git
+.gitignore
+.travis.yml
+.github
+*.md
+*.sh
+*.go
+go.mod
+go.sum
+bin/
+dist/
+examples/
+scripts/
+docs/
+*.tf
+terraform.tfstate*
+.terraform/
+.DS_Store
+*.log
+*.backup
+Makefile
+GNUmakefile
+GORELEASER_GPGSIGNING_PLAN.md
+TERRAFORM_BINARY_OPTIMIZATION_PLAN.md
+TESTCONTAINERS_*.md
+TIDB_*.md
+WORKFLOW_OPTIMIZATION_ANALYSIS.md
+terraform-registry-manifest.json
+VERSION

mysql/testcontainers_helper.go

@@ -600,15 +600,13 @@ func startSharedTiDBClusterWithTiUP(version string) (*TiDBTestCluster, error) {
 		return nil, fmt.Errorf("Dockerfile.tiup-playground not found at %s (moduleRoot=%s): %v", dockerfilePath, moduleRoot, err)
 	}
 
-	// Use a consistent image tag for caching
-	imageTag := fmt.Sprintf("terraform-provider-mysql-tiup-playground:latest")
-
 	req := testcontainers.ContainerRequest{
 		FromDockerfile: testcontainers.FromDockerfile{
 			Context:       moduleRoot,
 			Dockerfile:    "Dockerfile.tiup-playground",
-			PrintBuildLog: true,     // Helpful for debugging
-			Tag:           imageTag, // Use consistent tag for caching
+			PrintBuildLog: true, // Helpful for debugging
+			// Don't set Tag - let testcontainers generate its own tag format
+			// Setting Tag causes invalid format like UUID:TAG:latest
 		},
 		ExposedPorts: []string{"4000/tcp"},
 		// TiUP Playground needs to run processes and requires elevated capabilities