chore: stop tracking perf/raw.json (regenerated benchmark output)

raw.json gets fully rewritten by every perf run and the diff is essentially
symmetric (~190 insertions / ~190 deletions per run, all timing noise), so
it shows up as dirty in every working tree and pollutes every diff.

Curated/baseline perf snapshots (baseline.json, after.json, dedup.json) are
still tracked - those represent intentional comparisons and should change
deliberately.

Author: dougrathbone

.gitignore

@@ -9,3 +9,8 @@ tools/migration-labels.json
 tools/renames.json
 tools/cbus-labels-backup-*.json
 toolkit-certs/
+
+# Benchmark raw output regenerates with timing noise on every run.
+# Curated/baseline perf snapshots (baseline.json, after.json, dedup.json) are
+# still tracked intentionally.
+perf/raw.json