fix(docker): bake blender_path into EditorSettings for headless import

Godot's headless --import/--export-release refuses to auto-detect Blender
for .blend import: "Blender path is invalid or not set... Cannot configure
blender path in headless mode" (modules/gltf/editor/editor_scene_importer_blend.cpp).
Without this, the image's Blender install was silently unusable for its one
job — no .blend file would ever import in CI.

Bakes filesystem/import/blender/blender_path into a per-minor-version
EditorSettings .tres, same pattern barichello/godot-ci and abarichello's own
Dockerfile use for Android SDK/JDK paths.

Found and verified while resolving ticket #9 (Merge, publish, and validate
the debian-slim image end-to-end): confirmed a .blend import produces a real
.scn with this fix, and fails without it, on a real container built from
this Dockerfile.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Dockerfile

@@ -47,4 +47,16 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
   && mkdir -p /opt/blender \
   && tar -xJf /tmp/blender.tar.xz -C /opt/blender --strip-components=1 \
   && ln -sf /opt/blender/blender /usr/local/bin/blender \
-  && rm /tmp/blender.tar.xz
+  && rm /tmp/blender.tar.xz \
+  # Godot's headless `--import`/`--export-release` refuses to auto-detect Blender for .blend
+  # import ("Blender path is invalid or not set... Cannot configure blender path in headless
+  # mode") — it has to be pre-baked into EditorSettings, same as barichello/godot-ci bakes
+  # Android SDK/JDK paths into its editor_settings.tres. Settings are stored per minor version
+  # since Godot 4.3 (see abarichello/godot-ci's own Dockerfile for this same pattern).
+  && mkdir -p /root/.config/godot \
+  && printf '%s\n' \
+    '[gd_resource type="EditorSettings" format=3]' \
+    '' \
+    '[resource]' \
+    'filesystem/import/blender/blender_path = "/usr/local/bin/blender"' \
+    > "/root/.config/godot/editor_settings-${GODOT_VERSION%.*}.tres"