Add first-class native image operations

[JSv4]

Closes #453.

Summary

• adds owner-aware image inspection and native insert/replace/dimension/metadata/floating-layout/remove operations
• manages embedded and linked relationships across body, headers, footers, notes, comments, and table cells with package-wide deduplication and orphan cleanup
• extends snapshots so undo, redo, atomic rollback, and dry-run restore exact media bytes, relationship IDs, targets, and OPC part URIs
• keeps VML, linked, multi-picture, AlternateContent, and unmodeled floating layouts explicitly read-only
• exposes strict WASM, npm, Python, and MCP transports plus runtime capability metadata and architecture docs

Validation

• 23 image tests
• 597 broad DocxSession tests
• 65 MCP dispatcher tests
• focused independent image/MCP run: 88 tests
• core, WASM, MCP, and Python-host builds
• npm typecheck
• Python image transport test
• LibreOffice open/export smoke with raster verification

This is a stacked draft based on #451. The final epic linearization will place #445/#446 below it and adapt its batch/preview hooks to those shared transaction seams.