feat(platform): 日志管理 - 统一日志出口并屏蔽查询与 Agent 流式事件日志

新增 internal/logging，slog、标准库 log、GORM 与 Gin 访问日志共用同一 Handler，由 CANVAS_LOG_LEVEL / CANVAS_LOG_FORMAT 控制。info 级别不再输出成功的查询类请求、成功 SQL、message_end 等 Agent 流式事件和常规画布自动保存；4xx/5xx、慢请求、慢 SQL、SQL 失败与 panic 仍会记录，SQL 不内联参数值。

backend/internal/logging/http.go

@@ -0,0 +1,111 @@
+package logging
+
+import (
+	"io"
+	"log/slog"
+	"net/http"
+	"runtime/debug"
+	"strings"
+	"time"
+
+	"github.com/gin-gonic/gin"
+)
+
+// quietWriteSuffixes 是语义上只读、但用 POST 发出的高频路由（心跳、状态查询、批量读取）。
+// 与 GET 一样，成功时只在 debug 级别输出。
+var quietWriteSuffixes = []string{
+	"/heartbeat",
+	"/query",
+	"/query-provider",
+	"/query-task",
+	"/checkout/refresh",
+	"/assets/batch",
+	"/announcements/read",
+	"/diagnostics/preview",
+	"/system-update/check",
+}
+
+// AccessLog 替代 gin.Logger：成功的查询类请求（GET/HEAD/OPTIONS 与 quietWriteSuffixes）降为 debug，
+// 写请求记 info，4xx 记 warn，5xx 记 error；超过慢请求阈值的非流式请求无论方法都记 warn。
+// redactPath 用于脱敏 URL 中的凭据段（例如分享 token），为 nil 时原样输出。
+func AccessLog(redactPath func(string) string) gin.HandlerFunc {
+	return func(c *gin.Context) {
+		start := time.Now()
+		c.Next()
+		latency := time.Since(start)
+		status := c.Writer.Status()
+		route := c.FullPath()
+		level := accessLevel(c.Request.Method, route, status, latency, isStreamResponse(c))
+		ctx := c.Request.Context()
+		if !slog.Default().Enabled(ctx, level) {
+			return
+		}
+		path := c.Request.URL.Path
+		if redactPath != nil {
+			path = redactPath(path)
+		}
+		attrs := []slog.Attr{
+			slog.String("method", c.Request.Method),
+			slog.String("path", path),
+			slog.Int("status", status),
+			slog.Int64("latency_ms", latency.Milliseconds()),
+			slog.String("ip", c.ClientIP()),
+		}
+		if requestID := c.Writer.Header().Get("X-Request-ID"); requestID != "" {
+			attrs = append(attrs, slog.String("request_id", requestID))
+		}
+		if message := c.Errors.ByType(gin.ErrorTypePrivate).String(); message != "" {
+			attrs = append(attrs, slog.String("error", strings.TrimSpace(message)))
+		}
+		slog.LogAttrs(ctx, level, "http request", attrs...)
+	}
+}
+
+func accessLevel(method, route string, status int, latency time.Duration, stream bool) slog.Level {
+	switch {
+	case status >= http.StatusInternalServerError:
+		return slog.LevelError
+	case status >= http.StatusBadRequest:
+		return slog.LevelWarn
+	}
+	if threshold := slowRequestThreshold(); threshold > 0 && !stream && latency >= threshold {
+		return slog.LevelWarn
+	}
+	if isQueryRequest(method, route) {
+		return slog.LevelDebug
+	}
+	return slog.LevelInfo
+}
+
+func isQueryRequest(method, route string) bool {
+	switch method {
+	case http.MethodGet, http.MethodHead, http.MethodOptions:
+		return true
+	case http.MethodPost:
+		for _, suffix := range quietWriteSuffixes {
+			if strings.HasSuffix(route, suffix) {
+				return true
+			}
+		}
+	}
+	return false
+}
+
+// SSE 与分块下载天然是长连接，耗时不代表慢。
+func isStreamResponse(c *gin.Context) bool {
+	return strings.Contains(c.Writer.Header().Get("Content-Type"), "text/event-stream")
+}
+
+// Recovery 替代 gin.Recovery：panic 与堆栈进入统一日志，而不是直接写带颜色码的 stderr。
+func Recovery() gin.HandlerFunc {
+	return gin.CustomRecoveryWithWriter(io.Discard, func(c *gin.Context, recovered any) {
+		slog.ErrorContext(c.Request.Context(), "http panic recovered",
+			"method", c.Request.Method,
+			"route", c.FullPath(),
+			"request_id", c.Writer.Header().Get("X-Request-ID"),
+			"panic", recovered,
+			"stack", string(debug.Stack()),
+		)
+		c.AbortWithStatus(http.StatusInternalServerError)
+	})
+}