chore(ci): ignore benchmark and working-note scratch dirs

plans/, tb-*/** and terminal-bench/ are local-only working notes and
benchmark scratch, never committed. They leaked into CI's
'bunx oxfmt --check .' (static-analysis) scan, failing every PR that
picks them up from the environment. Ignore them so oxfmt scans only
trackable source.

Author: TheGreatAxios

.gitignore

@@ -30,6 +30,14 @@ subagents/
 
 # Working notes and design spikes — local only, never committed
 docs/plans/
+# Fleet/harness working notes — local only, never committed
+plans/
+
+# Benchmark/eval scratch — local only, never committed
+tb-dataset/
+tb-rerun-50/
+terminal-bench/
+evals/**/__pycache__/
 
 # Scratch repro tests — never committed
 __repro/