fix(log): ES 7.2.0 time format .SSSZ + index dropdown + demo always visible

- ES query 502 fix: remove +00:00 conversion, use native .SSSZ format
  (ES 7.2.0 date_time = strict_date_optional_time only, rejects +00:00/epoch)
- parseLogTime: use time.RFC3339Nano for fractional seconds
- new API GET /log-datasources/indices to list ES indices via proxy
- LogDatasourceDialog: add '获取索引' button + Select dropdown for ES
- LogDatasourcePage: always show demo sources alongside real ones

backend/controller/log_datasource.go

@@ -3,6 +3,7 @@ package controller
 import (
 	"crypto/tls"
 	"encoding/base64"
+	"encoding/json"
 	"io"
 	"net/http"
 	"strings"
@@ -168,6 +169,52 @@ func (h *LogDSHandler) TestConnection(c *gin.Context) {
 	c.JSON(200, model.Response{Code: 200, Message: "连接成功", Data: map[string]string{"status": "ok"}})
 }
 
+// ListIndices GET /api/v1/log-datasources/indices?url=...&type=elasticsearch
+// 通过代理查询 ES 集群的索引列表 // Logan.Li
+func (h *LogDSHandler) ListIndices(c *gin.Context) {
+	esURL := c.Query("url")
+	if esURL == "" {
+		c.JSON(400, model.Response{Code: 400, Message: "url 参数必填"})
+		return
+	}
+	basicAuth := c.Query("basic_auth") == "true"
+	user := c.Query("basic_auth_user")
+	pass := c.Query("basic_auth_pass")
+	skipTLS := c.Query("skip_tls_verify") == "true"
+
+	client := newLogHTTPClient(skipTLS, 10*time.Second)
+	target := strings.TrimRight(esURL, "/") + "/_cat/indices?format=json&h=index"
+	httpReq, err := http.NewRequest(http.MethodGet, target, nil)
+	if err != nil {
+		c.JSON(502, model.Response{Code: 502, Message: err.Error()})
+		return
+	}
+	applyLogDSAuth(httpReq, basicAuth, user, pass)
+	resp, err := client.Do(httpReq)
+	if err != nil {
+		c.JSON(502, model.Response{Code: 502, Message: "查询索引失败: " + err.Error()})
+		return
+	}
+	defer resp.Body.Close()
+	body, _ := io.ReadAll(resp.Body)
+	if resp.StatusCode >= 400 {
+		c.JSON(502, model.Response{Code: 502, Message: "ES 错误: " + string(body)})
+		return
+	}
+	var raw []map[string]interface{}
+	if err := json.Unmarshal(body, &raw); err != nil {
+		c.JSON(502, model.Response{Code: 502, Message: "解析索引列表失败"})
+		return
+	}
+	indices := make([]string, 0, len(raw))
+	for _, entry := range raw {
+		if idx, ok := entry["index"].(string); ok {
+			indices = append(indices, idx)
+		}
+	}
+	c.JSON(200, model.Response{Code: 200, Data: indices})
+}
+
 func testLogDSConnection(req model.TestLogDSReq) (bool, string) {
 	client := newLogHTTPClient(req.SkipTLSVerify, 10*time.Second)
 	url := strings.TrimRight(req.URL, "/")