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/handler/settings_handler_test.go

@@ -7,6 +7,7 @@ import (
 	"os"
 	"path/filepath"
 	"testing"
+	"time"
 
 	"github.com/gin-gonic/gin"
 	"github.com/stretchr/testify/assert"
@@ -416,3 +417,94 @@ func TestSettingsHandler_SaveStartupSettings_InvalidJSON(t *testing.T) {
 
 	assert.Equal(t, 400, w.Code)
 }
+
+func TestSettingsHandler_GetStartupSettings_DurationNormalization(t *testing.T) {
+	cfg, configPath := createTestConfig(t)
+
+	yamlContent := `
+server:
+  port: 9826
+  read_timeout: 30s
+  write_timeout: 1m
+database:
+  driver: sqlite
+  path: ` + cfg.Database.Path + `
+  max_idle_conns: 10
+  max_open_conns: 100
+  conn_max_lifetime: 30m
+log:
+  level: info
+  path: ` + cfg.Log.Path + `
+  max_size: 100
+  max_backups: 10
+  max_age: 30
+  compress: true
+`
+	require.NoError(t, os.WriteFile(configPath, []byte(yamlContent), 0o600))
+
+	h := NewSettingsHandler(cfg, "desktop", true, configPath)
+
+	w := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(w)
+	c.Request = httptest.NewRequest("GET", "/api/settings/startup", nil)
+
+	h.GetStartupSettings(c)
+
+	assert.Equal(t, 200, w.Code)
+
+	var resp startupSettingsResponse
+	require.NoError(t, json.Unmarshal(w.Body.Bytes(), &resp))
+	assert.Equal(t, "1m0s", resp.Config.Server.WriteTimeout)
+	assert.Equal(t, "30m0s", resp.Config.Database.ConnMaxLifetime)
+}
+
+func TestSettingsHandler_SaveStartupSettings_StandardDurationRoundTrip(t *testing.T) {
+	cfg, configPath := createTestConfig(t)
+	h := NewSettingsHandler(cfg, "desktop", true, configPath)
+
+	tmpDir := t.TempDir()
+	body, _ := json.Marshal(map[string]interface{}{
+		"config": map[string]interface{}{
+			"server": map[string]interface{}{
+				"port":          9826,
+				"read_timeout":  "30s",
+				"write_timeout": "1m0s",
+			},
+			"database": map[string]interface{}{
+				"driver":            "sqlite",
+				"path":              filepath.Join(tmpDir, "test.db"),
+				"port":              3306,
+				"dbname":            "nex",
+				"max_idle_conns":    10,
+				"max_open_conns":    100,
+				"conn_max_lifetime": "1h0m0s",
+			},
+			"log": map[string]interface{}{
+				"level":       "info",
+				"path":        filepath.Join(tmpDir, "log"),
+				"max_size":    100,
+				"max_backups": 10,
+				"max_age":     30,
+				"compress":    true,
+			},
+		},
+	})
+
+	w := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(w)
+	c.Request = httptest.NewRequest("PUT", "/api/settings/startup", bytes.NewReader(body))
+	c.Request.Header.Set("Content-Type", "application/json")
+
+	h.SaveStartupSettings(c)
+
+	assert.Equal(t, 200, w.Code)
+
+	var resp startupSettingsResponse
+	require.NoError(t, json.Unmarshal(w.Body.Bytes(), &resp))
+	assert.Equal(t, "1m0s", resp.Config.Server.WriteTimeout)
+	assert.Equal(t, "1h0m0s", resp.Config.Database.ConnMaxLifetime)
+
+	savedCfg, err := config.LoadDesktopConfigAtPath(configPath)
+	require.NoError(t, err)
+	assert.Equal(t, 1*time.Hour, savedCfg.Database.ConnMaxLifetime)
+}