Merge branch 'origin/master' - combine double-execution fixes

Both branches fixed the --exec double-execution bug with complementary approaches:
- origin/master: Added executeStartupScripts() method for cleaner separation
- HEAD: Avoided engine recreation to preserve state

This merge keeps the best of both: executeStartupScripts() called on the
existing engine without recreation.

Also accepts deletion of flaky test_viewport_visual.py from origin/master.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/main.cpp

@@ -183,8 +183,8 @@ int run_python_interpreter(const McRogueFaceConfig& config)
         return 0;
     }
     else if (!config.exec_scripts.empty()) {
-        // With --exec, scripts were already executed by the first GameEngine constructor.
-        // Just configure auto-exit and run the existing engine to preserve timers/state.
+        // Execute startup scripts on the existing engine (not in constructor to prevent double-execution)
+        engine->executeStartupScripts();
         if (config.headless) {
             engine->setAutoExitAfterExec(true);
         }