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/smoke-checklist.md

@@ -39,4 +39,4 @@
 37. The F debug overlay lists the next eligible events; recovery events and recently played scripted events behave as authored.
 38. Master/SFX/ambience volume settings clamp at 0/1 and persist; Reduce motion disables head bob; the captions toggle persists.
 39. The 24-NPC budget smoke stays inside its frame budget; coats/dresses do not show obvious leg clipping in a normal walk.
-40. Help remains readable with the largest HUD font scale, and the engine matrix (4.3 CI / 4.7.2 local) is used for verification.
+40. Help remains readable with the largest HUD font scale, and CI/local verification use the same Godot 4.7.2 baseline.