fix(strategy): print a summary for --compare --quiet instead of nothing

[statxc]

PR kind

• fix
• feat

Summary

strategy --compare --quiet produced no output at all. runner.compare() only prints its report when verbose (i.e. not --quiet), and main() discarded compare()'s return value and return 0'd before the --quiet summary block that the normal run path has:

if args.compare:
    runner.compare(...)   # prints nothing under --quiet
    return 0              # <- before the quiet-summary block

So a scripted --compare --quiet run silently computed both engines and printed nothing.

Fix

Capture compare()'s returned dict and, under --quiet, print a one-line summary (exact/smart seconds, speedup, rel_err) — mirroring the run path's --quiet line. Non-quiet behaviour is unchanged (compare() still prints its full report; no double output).

Touches only strategy/cli.py and a new test — no protected paths.

Validation

uv run --extra test python -m pytest tests/test_compare_quiet.py -q             # 2 passed
uv run --extra test python -m pytest tests/ strategy/tests/ eval/tests/ -q      # 283 passed, 24 skipped

The test stubs runner.compare via monkeypatch, so it runs on CPU with no GPU/torch — it exercises the flag handling and summary formatting (and asserts non-quiet mode does not double-print).

Checklist

• CPU-safe validation passed.
• My commits do not include Co-authored-by footers for coding agents such as Cursor, Codex, Claude, Copilot, or similar tools.
• Not a feat PR — no scorecard required.

[zeokin]

--compare --quiet now prints a one-line summary instead of nothing; no double-print.