[WIP] Add per-sheet include/exclude controls for incremental workbook encoding

[Claude]

Thanks for asking me to work on this. I will get started on it and keep this PR's description up to date as I form a plan and make progress.

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This section details on the original issue you should resolve

<issue_title>Add per-sheet include/exclude controls for incremental workbook encoding</issue_title>
<issue_description>## Problem
Some real workbooks contain many sheets with very different sizes. Users may need to encode only a relevant subset instead of paying the cost of every sheet in one run.

Why this matters

During smoke testing, one workbook contained many small sheets plus a very large 3214x110 sheet. Per-sheet controls would allow users to inspect or process the useful sheets immediately while deferring the expensive sheet.

Proposed work

• Add CLI flags such as --include-sheet, --exclude-sheet, or glob/regex variants.
• Add equivalent Python API parameters.
• Record included/excluded sheet names in output metadata.
• Make evaluation and downstream prompt code tolerate deliberately omitted sheets.

Acceptance criteria

• Users can encode one named sheet from a multi-sheet workbook.
• Users can exclude one expensive sheet and encode the rest.
• Output metadata lists skipped sheets and skip reasons.
• Tests cover CLI and Python API filtering.</issue_description>
• Closes Add per-sheet include/exclude controls for incremental workbook encoding #34

Comments on the Issue (you are @claude[agent] in this section)

@kingkillery @claude @kingkillery @copilot

• Fixes Add per-sheet include/exclude controls for incremental workbook encoding #34