Fix stacked camera cleanup order

[FxckingAngel]

Summary

• Fix stacked camera teardown so every camera in the stack is destroyed.
• Iterate backwards when removing cameras from the backing list.

Why

DestroyCameraStack previously iterated forward while DestroyCamera removed entries from _cameras. With more than one stacked camera, removing index 0 shifts the next camera down and the loop can skip it, leaving a camera GameObject alive after teardown.

This keeps cleanup deterministic and avoids leaving extra cameras/rendering work around after the stacked camera system is disabled.

Testing

• Not run locally; this repository snapshot does not include a runnable Unity test project in main.

Related to #95.

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[FxckingAngel]

Closing this for now while I revise the approach.