fix: Attack file schema for burn_lp needs documentation and migration (#615)

Add SCHEMA.md documenting the JSONL attack file format with all operation
definitions, field types, and the burn_lp tokenId convention divergence
between AttackRunner (.positionIndex) and FitnessEvaluator (.tokenId).

Add schema-version header comments to all existing attack files and teach
both consumers to skip comment lines starting with //.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

onchain/script/backtesting/attacks/staking-safe.jsonl

@@ -1,3 +1,4 @@
+// schema-version: 1
 {"op":"buy","amount":"50000000000000000000","token":"WETH"}
 {"op":"recenter"}
 {"op":"stake","amount":"1000000000000000000000","taxRateIndex":0}