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.

README.md

@@ -74,7 +74,7 @@ decisions are recorded as ADRs in [`docs/adr/`](docs/adr/).
 
 ## Tech Stack
 
-- **Engine:** Godot 4.3 baseline (local dev verified with 4.7.2) · **Language:** GDScript
+- **Engine:** Godot 4.7.2 · **Language:** GDScript
 - **NPCs:** Blender-authored skinned library (`assets/models/blender/`) with procedural fallbacks; lightweight FSMs on `NpcProfile`
 - **World:** procedural `WorldBuilder` + generated prop models
 - **Art:** v2 skyline/surface textures in `assets/textures/ai/game_ready/v2/picks/`; UI/scene art in `assets/images/`
@@ -119,7 +119,7 @@ Full setup, every run/test/smoke command, and the controls table are in
 ## Development Status
 
 v0.9.0 adds the production-quality baseline: mixer/accessibility settings, a
-24-NPC performance budget and the documented Godot 4.3-CI/4.7-local matrix, on
+24-NPC performance budget and the unified Godot 4.7.2 toolchain, on
 top of v0.8's tutorial, campaign, checkpoint resume, difficulty and Help. See
 [`docs/development-status.md`](docs/development-status.md) for the implemented
 list and [`TODO.md`](TODO.md) for the v1.0.0 roadmap. Manual verification uses