fix: 启动参数 duration 候选值对齐后端标准格式

前端 Select 使用 Go time.Duration.String() 标准字符串作为 value，
与后端查询/保存响应保持一致，解决保存后反显不匹配的问题。

backend/internal/config/config_metadata_test.go

@@ -66,6 +66,63 @@ func TestDurationConversion(t *testing.T) {
 	assert.Equal(t, cfg.Database.ConnMaxLifetime, parsed)
 }
 
+func TestSaveConfigToPath_DurationFormat(t *testing.T) {
+	dir := t.TempDir()
+	configPath := filepath.Join(dir, "config.yaml")
+
+	cfg := DefaultConfig()
+	cfg.Server.ReadTimeout = 30 * time.Second
+	cfg.Server.WriteTimeout = 1 * time.Minute
+	cfg.Database.ConnMaxLifetime = 1 * time.Hour
+
+	err := SaveConfigToPath(cfg, configPath)
+	require.NoError(t, err)
+
+	data, err := os.ReadFile(configPath)
+	require.NoError(t, err)
+	content := string(data)
+	assert.Contains(t, content, "conn_max_lifetime: 1h0m0s")
+	assert.Contains(t, content, "read_timeout: 30s")
+	assert.Contains(t, content, "write_timeout: 1m0s")
+}
+
+func TestSaveAndReload_DurationRoundTrip(t *testing.T) {
+	dir := t.TempDir()
+	configPath := filepath.Join(dir, "config.yaml")
+
+	yamlContent := `
+server:
+  port: 9826
+  read_timeout: 30s
+  write_timeout: 1m
+database:
+  driver: sqlite
+  path: ` + filepath.Join(dir, "test.db") + `
+  max_idle_conns: 10
+  max_open_conns: 100
+  conn_max_lifetime: 30m
+log:
+  level: info
+  path: ` + filepath.Join(dir, "log") + `
+  max_size: 100
+  max_backups: 10
+  max_age: 30
+  compress: true
+`
+	require.NoError(t, os.WriteFile(configPath, []byte(yamlContent), 0o600))
+
+	cfg, err := LoadDesktopConfigAtPath(configPath)
+	require.NoError(t, err)
+	assert.Equal(t, 30*time.Minute, cfg.Database.ConnMaxLifetime)
+
+	err = SaveConfigToPath(cfg, configPath)
+	require.NoError(t, err)
+
+	data, err := os.ReadFile(configPath)
+	require.NoError(t, err)
+	assert.Contains(t, string(data), "conn_max_lifetime: 30m0s")
+}
+
 func configToDTO(c *Config) struct {
 	Server struct {
 		Port         int    `json:"port"`