fix(auth): add JSON tags to AccessSnapshot fields for proper serialization

internal/auth/access_tracker.go

@@ -7,12 +7,12 @@ import (
 )
 
 type AccessSnapshot struct {
-	KeyID          string
-	LastPath       string
-	RemoteAddr     string
-	UserAgent      string
-	RequestCount   int
-	LastAccessedAt time.Time
+	KeyID          string    `json:"key_id"`
+	LastPath       string    `json:"last_path"`
+	RemoteAddr     string    `json:"remote_addr"`
+	UserAgent      string    `json:"user_agent"`
+	RequestCount   int       `json:"request_count"`
+	LastAccessedAt time.Time `json:"last_accessed_at"`
 }
 
 type AccessTracker struct {