Move eval module out of `src/sre_agent/` into top-level `evals/`

[osw282]

Summary

The eval module currently lives at src/sre_agent/eval/, which means it gets bundled into the distributed wheel alongside production code (cli, config, core). Evaluation/benchmark code is a dev-time concern and should not ship with the package.

Proposed Changes

1. Move src/sre_agent/eval/ → evals/ at the project root (alongside tests/, docs/, etc.)
2. Remove the eval entry points from [project.scripts] in pyproject.toml:
   • sre-agent-run-tool-call-eval
   • sre-agent-run-diagnosis-quality-eval
3. Update invocation to run evals as standalone scripts (e.g. python -m evals.tool_call.run) or via a Makefile/task runner target.
4. Update any CI/docs that reference the old paths or entry points.

Motivation

• Smaller production package — eval code, fixtures, and eval-only dependencies don't belong in the shipped wheel.
• Separation of concerns — keeps src/sre_agent/ focused on the agent itself.
• Convention — matches the common pattern of top-level tests/, evals/, benchmarks/ directories.