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/RELEASING.md

@@ -12,11 +12,11 @@ time you export, either:
   matching templates), or
 - Install them manually from the
   [Godot downloads](https://godotengine.org/download/) page by placing the
-  `Godot_v4.3-stable_export_templates.tpz` contents into
-  `~/.local/share/godot/export_templates/4.3.stable/`.
+  `Godot_v4.7.2-stable_export_templates.tpz` contents into
+  `~/.local/share/godot/export_templates/4.7.2.stable/`.
 
-The templates must match the editor binary you use locally. CI pins Godot 4.3;
-the local development machine uses 4.7.2 with its matching templates. Verify with:
+The templates must match the editor binary you use locally. CI and local
+development both use Godot 4.7.2 with its matching templates. Verify with:
 
 ```bash
 godot --headless --export-release "Linux" build/gig-line-smoke.x86_64
@@ -31,7 +31,7 @@ godot --headless --export-release "Linux" build/gig-line-smoke.x86_64
 
 The repository ships a Gitea Actions workflow (`.gitea/workflows/build.yml`):
 
-- Every push/PR runs the **checks** job: Godot 4.3 install, project import, and the
+- Every push/PR runs the **checks** job: Godot 4.7.2 install, project import, and the
   full headless test suite. This is the fast safety net.
 - **Tags (`v*`)** and **manual `workflow_dispatch`** runs additionally execute the
   **build** job: export templates install, import, `tools/build_releases.sh` for
@@ -63,10 +63,10 @@ setup, so do not rely on it.
 > artifacts. If CI publishing fails again, run
 > `./tools/publish_release.sh <version>` from a checkout with `~/.git-credentials`.
 
-> **No `actions/cache` for now:** the runner has no local actions-cache service, so
-> `actions/cache` times out against GitHub's cache API. We dropped it (Godot import
-> is only ~4s). If a host admin later enables Gitea `[cache.actions]` with a cache
-> server, the step can be reintroduced.
+> **Godot cache:** the workflow uses Gitea Actions cache for the Godot binary and the
+> 4.7.2 export templates. The first run still downloads them; subsequent runs restore
+> from cache. If the host cache service is unavailable, remove the cache steps and
+> let the install steps download fresh copies.
 
 > The workflow lives in `.gitea/workflows/` (Gitea's canonical path). The old
 > `.github/workflows/ci.yml` was removed to avoid double runs on hosts that scan