Untrack soak CSVs - generated artifacts, not source

The soak_*.csv debug outputs are regenerated every run and were churning
thousands of lines per commit (npc_days.csv alone is 730KB, fully
overwritten each run). Findings live curated in FINDINGS.md, so the raw
CSVs and their Godot .import metadata don't belong in history. Ignored
going forward; files stay on disk so runs are unaffected. Also tracks
the SpatialGrid script UID.

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

.gitignore

@@ -7,3 +7,7 @@ export_presets.cfg
 bin/
 obj/
 *.csproj.user
+
+# Soak-test outputs — regenerated every run; findings are curated in FINDINGS.md
+soak_*.csv
+soak_*.csv.import