Unify the Godot 4.7.2 CI environment and cache it

Update project features and CI installs/templates to Godot 4.7.2, remove the
old version matrix, and cache the Godot binary and export templates with Gitea
Actions cache. Update release/docs/version references accordingly. Project
import and headless tests pass locally under 4.7.2.

docs/getting-started.md

@@ -2,7 +2,7 @@
 
 ## Setup
 
-1. Download the Godot 4.3+ editor (official build) and put `godot` on your PATH. The supported policy is an explicit matrix: CI/release baseline 4.3, local development verified with 4.7.2. Engine upgrades require import, headless, screenshot and Desktop HQ smoke checks before changing the baseline.
+1. Download Godot **4.7.2** (official build) and put `godot` on your PATH. The project, local tooling and CI use the same version; engine upgrades require import, headless, screenshot and Desktop HQ smoke checks before changing the baseline.
 2. Open or run the project from this directory.
 
 ## Run and Test