feat(office): add transactional XLSX create and batch

[bobzhang]

Summary

• add a reusable async fresh-package transaction with bounded validation and atomic publication
• add strict resource-accounted xlsx.batch/1 plans and a shared transactional XLSX mutation SDK
• expose canonical office create xlsx and office batch commands with versioned JSON results, capability discovery, and stable errors
• reuse the strict plan parser in the legacy XLSX CLI
• cover native/Wasm behavior, Cram CLI flows, and Microsoft DocumentFormat.OpenXml validity

Why

This closes the X3 parity gap with OfficeCLI while keeping mutation safety, limits, and publication semantics in one future-proof transaction boundary. It uses moonbitlang/async throughout and introduces no C stubs.

Impact

Agents can now create validated XLSX packages and apply bounded multi-operation scripts atomically. Creation is no-replace by default, separate batch outputs require explicit overwrite, dry runs perform full validation, zero-op in-place batches preserve source bytes, and changed batches report full-workbook rewrite preservation evidence.

This is stacked on #172 (agent/office-x2-xlsx-read) so the PR diff contains only X3. Merge #172 first, then retarget this PR to main.

Validation

• moon info && moon fmt (source clean; known moon.pkg formatter migration restored)
• moon check
• moon check --target wasm
• moon test --target native — 4,938 passed
• moon test --target wasm — 4,284 passed
• focused batch/Office/XLSX native, Wasm, and JS suites
• Office CLI Cram — 127 passed
• Microsoft DocumentFormat.OpenXml SDK acceptance — passed
• native and Wasm CLI create/batch/readback smoke tests

Closes #162