chore(config): add spike gitignore rules and Blender wrapper

Add .gitignore entries for spike Godot caches, import artifacts,
and vendor asset downloads. Add tooling/blender wrapper that resolves
flatpak/native Blender installs and auto-converts relative paths to
absolute for flatpak sandbox compatibility.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.gitignore

@@ -20,6 +20,14 @@ renderer/**/*.import
 renderer/**/*.uid
 renderer/output/*.png
 
+# Spikes (Godot cache + import artifacts)
+spikes/**/.godot/
+spikes/**/*.import
+spikes/**/*.uid
+
+# Asset downloads (vendor archives, not game content)
+docs/assets/downloads/
+
 # Database (shared across worktrees at ../settledreach.db, not tracked)
 db/commonwealth.db*