feat(docx): support cross-document paragraph cloning with source formatting

## Problem

`officecli add --from ` can clone a paragraph only within the same DOCX file. When an agent needs to assemble a new document from existing Word documents, the available paragraph-level `dump`/`batch` path does not carry sibling document resources such as styles, numbering, and theme definitions. As a result, copying a paragraph into a new DOCX cannot reliably match Word's **Keep Source Formatting** behavior.

## Proposed interface

Add an explicit source-document option, or an equivalent cross-document clone operation:

```powershell
officecli add target.docx /body `
--from-file source.docx `
--from "/body/p[12]" `
--after "/body/p[3]"
```

The source document should remain read-only.

## Expected behavior

For a copied Word paragraph:

- preserve paragraph properties and all child runs/direct character formatting;
- import or remap referenced custom styles and numbering definitions;
- preserve theme-dependent appearance where required;
- copy and remap media and hyperlink relationships used by the paragraph;
- remap colliding bookmark, comment, footnote, endnote, drawing, and relationship IDs;
- reuse identical target definitions where safe and handle conflicting definitions deterministically;
- produce a DOCX that passes `officecli validate` and opens correctly in Microsoft Word.

## Motivation

This is useful for contract assembly, compliance-review summaries, report compilation, and other workflows that collect selected source paragraphs into a new Word document. Today agents can find the paragraph and clone it inside its original document, but cannot transfer it to a new document with source formatting intact.

A paragraph-first implementation would already cover the primary use case; support for tables and other block elements could follow separately.

Start with the officecli add command and its existing --from paragraph-cloning path, then compare the paragraph-level dump/batch workflow. Use the proposed --from-file interface as the starting point and run officecli validate on a copied paragraph; done means source formatting and referenced resources survive remapping and the result opens correctly in Word.

Written by the indexing model from the issue text.