refactor: switch config format from YAML to TOML

- Replace gopkg.in/yaml.v3 with github.com/BurntSushi/toml
- Update struct tags from yaml to toml
- Update config tests to use TOML syntax
- Add testdata/config.toml, update Helm configmap template

internal/config/config_test.go

@@ -7,20 +7,22 @@ import (
 )
 
 func TestLoad_MissingFile(t *testing.T) {
-	_, err := Load("/nonexistent/config.yaml")
+	_, err := Load("/nonexistent/config.toml")
 	if err == nil {
 		t.Fatal("expected error for missing file")
 	}
 }
 
 func TestLoad_MissingGitToken(t *testing.T) {
-	cfg := `server:
-  addr: ":8080"
-git:
-  type: gitea
-  base_url: "https://git.example.com"
-cluster:
-  namespace: proto-gen`
+	cfg := `[server]
+addr = ":8080"
+
+[git]
+type = "gitea"
+base_url = "https://git.example.com"
+
+[cluster]
+namespace = "proto-gen"`
 	path := writeTempConfig(t, cfg)
 	os.Setenv("GIT_TOKEN", "")
 	_, err := Load(path)
@@ -33,19 +35,22 @@ func TestLoad_ValidConfig(t *testing.T) {
 	os.Setenv("GIT_TOKEN", "test-token")
 	defer os.Unsetenv("GIT_TOKEN")
 
-	cfg := `server:
-  addr: ":9090"
-git:
-  type: gitea
-  base_url: "https://git.example.com"
-  token: ${GIT_TOKEN}
-cluster:
-  namespace: proto-gen
-  job_timeout: 300
-  max_concurrent: 3
-plugins:
-  - language: go
-    image: "proto-gen-go:v1.0"`
+	cfg := `[server]
+addr = ":9090"
+
+[git]
+type = "gitea"
+base_url = "https://git.example.com"
+token = "${GIT_TOKEN}"
+
+[cluster]
+namespace = "proto-gen"
+job_timeout = 300
+max_concurrent = 3
+
+[[plugins]]
+language = "go"
+image = "proto-gen-go:v1.0"`
 	path := writeTempConfig(t, cfg)
 
 	got, err := Load(path)
@@ -73,12 +78,13 @@ func TestLoad_DefaultValues(t *testing.T) {
 	os.Setenv("GIT_TOKEN", "test-token")
 	defer os.Unsetenv("GIT_TOKEN")
 
-	cfg := `git:
-  type: gitea
-  base_url: "https://git.example.com"
-  token: ${GIT_TOKEN}
-cluster:
-  namespace: proto-gen`
+	cfg := `[git]
+type = "gitea"
+base_url = "https://git.example.com"
+token = "${GIT_TOKEN}"
+
+[cluster]
+namespace = "proto-gen"`
 	path := writeTempConfig(t, cfg)
 
 	got, err := Load(path)
@@ -119,7 +125,7 @@ func TestGetPluginByLanguage(t *testing.T) {
 func writeTempConfig(t *testing.T, content string) string {
 	t.Helper()
 	dir := t.TempDir()
-	path := filepath.Join(dir, "config.yaml")
+	path := filepath.Join(dir, "config.toml")
 	if err := os.WriteFile(path, []byte(content), 0644); err != nil {
 		t.Fatalf("writing temp config: %v", err)
 	}