feat(read): add bounded sparse XLSX workbook support

[jieyuexing]

Summary

• add a native sparse OOXML reader for local .xlsx workbooks, with bounded previews and batched Sheet!A1:D20 range selection
• preserve structured workbook evidence including sheet visibility, semantic bounds, defined names, formulas and cached values, dates, merged-cell membership, range overflow, rich-text strike/color, print settings, and worksheet picture anchors
• expose revision-only probes, incremental WorkbookSession refresh, and generated Markdown mirror replacement without overwriting agent-authored regions
• publish the workbook artifact through the CLI machine protocol and Node facade, with cell, compressed-input, expanded-OOXML, image-payload, and serialized-output limits
• add compatibility documentation, corpus/read benchmark harnesses, Rust integration tests, CLI tests, and Node protocol validation

Safety and limits

• the reader does not recalculate formulas or execute macros
• legacy .xls, encrypted workbooks, chart reconstruction, image OCR, conditional-format rendering, and Excel-accurate visual rendering remain out of scope
• declared worksheet dimensions never cause dense rectangular allocation
• truncated reads retain valid structured output and explicit completeness/warning signals

Scope

This branch is based directly on the latest lencx/opsail:main and intentionally excludes the cookie-file and CLI-usage changes proposed separately in #5 and #6.

Testing

• cargo +1.97.0 fmt --all -- --check
• cargo +1.97.0 test --workspace --offline (279 passed)
• cargo +1.97.0 clippy --workspace --all-targets --offline -- -D warnings
• RUSTUP_TOOLCHAIN=1.97.0 npm test from packages/node (87 passed)