Add debug logging to GenerateRandomAPIKey in auth/apikey.go

Log function entry, success, and failure for GenerateRandomAPIKey using
the existing package-level debug logger (declared in auth/header.go).
This provides visibility into API key generation at startup when
DEBUG=auth:* is enabled.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: github-actions[bot]

internal/auth/apikey.go

@@ -10,9 +10,12 @@ import (
 // Per spec §7.3, the gateway SHOULD generate a random API key on startup
 // if none is provided. Returns a 32-byte hex-encoded string (64 chars).
 func GenerateRandomAPIKey() (string, error) {
+	log.Print("Generating random API key")
 	key, err := strutil.RandomHex(32)
 	if err != nil {
+		log.Printf("Random API key generation failed: %v", err)
 		return "", fmt.Errorf("failed to generate random API key: %w", err)
 	}
+	log.Print("Random API key generated successfully")
 	return key, nil
 }