docs(locomo): record v2-r13 evidence-driven no-op

[Cocoblood9527]

Summary

• run constrained offline A/B for three candidates: games, kind, names
• enforce acceptance rule: change code only if overall and multi-hop both improve
• record no-op decision in V2-R13 spec/plan/results docs

Test Plan

• cargo test --workspace
• ./.venv/bin/pytest python/tests -q
• corepack pnpm --dir packages/node test
• corepack pnpm --dir packages/mcp test
• REBUILD_PYTHON=0 tools/locomo/run-full-gate.sh 5