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/GameEngine.h

@@ -146,6 +146,7 @@ public:
     void run();
     void sUserInput();
     void cleanup(); // Clean up Python references before destruction
+    void executeStartupScripts(); // Execute --exec scripts (called once after final engine setup)
     int getFrame() { return currentFrame; }
     float getFrameTime() { return frameTime; }
     sf::View getView() { return visible; }