Update to Configuration Version 9

[KaceCottam]

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1. What it changes
2. Why it's needed

What does this PR change?

Updates the export schema to address the latest version of TrenchBroom.

According to: the manual for TrenchBroom 2025.3, the only change from configuration version 8->9 is: "Adapt to terminology change: texture renamed to material".

Modified README to include the latest TrenchBroom version as well as modified template strings in <addons/qodot/src/resources/game-definitions/trenchbroom_game_config.gd>, to change instances of "texture" to "material", or "textures" to "materials".

Does this pull request address an existing issue?

#163