fix(channelserver): post-RC1 stabilization sprint

Fix rasta_id=0 overwriting NULL in SaveMercenary, which prevented
game state saving for characters without a mercenary (#163).

Also includes:
- CHANGELOG updated with all 10 post-RC1 commits
- Setup wizard fmt.Printf replaced with zap structured logging
- technical-debt.md updated with 6 newly completed items
- Scenario binary format documented (docs/scenario-format.md)
- Tests: alliance nil-guard (#171), handler dispatch table,
  migrations (sorted/SQL/baseline), setup wizard (10 tests),
  protbot protocol sign/entrance/channel (23 tests)

server/setup/setup.go

@@ -30,8 +30,9 @@ func Run(logger *zap.Logger, port int) error {
 		Handler: r,
 	}
 
-	logger.Info(fmt.Sprintf("Setup wizard available at http://localhost:%d", port))
-	fmt.Printf("\n  >>> Open http://localhost:%d in your browser to configure Erupe <<<\n\n", port)
+	logger.Info("Setup wizard available",
+		zap.String("url", fmt.Sprintf("http://localhost:%d", port)))
+	logger.Warn("Open the URL above in your browser to configure Erupe")
 
 	// Start the HTTP server in a goroutine.
 	errCh := make(chan error, 1)