Use DeepSeek agent for BuffBench

[jahooma]

Summary

• Switch BuffBench main runner from base2-free-evals to base2-free-deepseek.

Validation

• Reviewed git diff origin/main...HEAD.

The stated change — swapping base2-free-evals for base2-free-deepseek in evals/buffbench/main.ts — is a one-line, sensible change and clearly in scope.

However the diff is much larger than the description suggests. agents/base2/base-deep.ts and agents/base2/base2.ts also drop file-picker, file-picker-max, directory-lister, and glob-matcher from spawnableAgents, rewrite the system/step prompts to point at glob/list_directory/read_subtree/read_files instead, and get a bunch of unrelated prettier-style reformatting (multi-line function signatures, template literal indentation). None of that is mentioned in the PR body, and there's no rationale given for retiring those sub-agents or reason to believe it's tied to the DeepSeek swap.

As it stands this reads like two unrelated changes squashed together: a trivial eval config change, and a meaningful behavioral change to how base2/base-deep orchestrate sub-agents. The latter deserves its own PR with a description of why those agents are being removed and what testing (if any) shows the direct-tool approach performs as well. Please split these so each can be reviewed and ported on its own merits.