feat: add parameter sweep command for variant generation and ranking

[claytonlin1110]

Summary

Closes #119

• add new paperbanana sweep CLI command to run a cartesian sweep across providers, models, iterations, and optimization/auto-refine modes
• add paperbanana/core/sweep.py with structured variant planning, CSV axis parsing, ranking, and summary helpers
• persist sweep outputs under sweep_<id>/variant_<id>/ and write sweep_report.json with per-variant status, runtime, and ranked results
• include dry-run mode to preview planned variants without API calls
• add tests for sweep core helpers and CLI dry-run / validation behavior

Motivation

One diagram depends on many settings (providers, models, iterations, optimize/auto-refine). Changing flags and comparing runs by hand is slow and easy to lose track of. A sweep runs those combinations in one go, writes a single ranked report, and supports dry-run so you can plan before spending API quota.

[claytonlin1110]

@dippatel1994 Would you please review this?

[claytonlin1110]

@dippatel1994 please review

[claytonlin1110]

@dippatel1994 Any update about this feature?

[dippatel1994]

CI passes, nice work. A few things to fix:

1. Settings constructed per-variant inside the loop — load_dotenv() should be called once before the loop, and Settings should be built once then copied with model_copy(update=overrides) per variant. Currently re-parses YAML on every iteration.

2. Missing --pdf-pages option — Every other command that accepts --input with PDF support also exposes --pdf-pages. The sweep command calls load_methodology_source(input_path) without it.

3. No non-dry-run test — Only --dry-run and validation are tested. Add a test that mocks the pipeline and verifies the sweep report structure (status, ranked results, timing). test_ablate_retrieval_writes_report is a good template.

Non-blocking: The quality proxy formula (100 - 12.5 * suggestions) is undocumented and fragile — consider at minimum documenting it in --help. Also missing --budget and --auto-download-data flags for parity with generate/batch.

[claytonlin1110]

Thank you for yuor feedback, @dippatel1994
Just updated PR

[dippatel1994]

All 3 points addressed. Settings built once with model_copy per variant, --pdf-pages added, non-dry-run test added. CI green. LGTM.

[claytonlin1110]

Thanks @dippatel1994
ready to be merged?