Move soak output to soak/ folder with .gdignore

CSVs now write to soak/ instead of the project root. A .gdignore there
stops the Godot editor from importing CSV columns as translation files -
which had been silently generating 50+ .translation and .import files per
run. Only the .gdignore is tracked; the CSVs stay ignored. Root is clean.

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

.gitignore

@@ -9,5 +9,6 @@ obj/
 *.csproj.user
 
 # Soak-test outputs — regenerated every run; findings are curated in FINDINGS.md
-soak_*.csv
-soak_*.csv.import
+soak/*.csv
+soak/*.csv.import
+soak/*.translation