Add first-class links and bookmarks (#451)

[JSv4]

Summary

• add typed read APIs for native hyperlinks and bookmarks, including owning part/scope, spans, visible text, targets, relationships, and malformed-state diagnostics
• add external/internal hyperlink CRUD and bookmark add/rename/move/remove across body, headers, footers, footnotes, and endnotes
• preserve bookmark/link boundaries through supported text, split, merge, move, and deletion operations while rejecting unsafe or tracked-only representations explicitly
• manage owner-local relationship reuse, cleanup, and undo/redo topology; fix internal Markdown links and cross-part relationship ownership (Internal hyperlinks round-trip into external relationships targeting a literal "#name" #469, Hyperlinks authored into a header, footer or note register their relationship on the main document part #470)
• expose the complete surface through .NET, WASM/npm, Python, and MCP with updated documentation

Validation

• 111 focused regression tests passed: all link/bookmark, move-block, and MCP dispatcher tests
• 23/23 dedicated link/bookmark tests passed after final audit
• OpenXmlValidator assertions cover saved packages and bookmark marker invariants
• LibreOffice DOCX→ODT→DOCX round-trip/reopen smoke check passed
• git diff --check and builds passed

Stack

This draft targets agent/issue-448-introspection (draft PR #477) so the review contains only issue #451 changes.

Closes #451
Fixes #469
Fixes #470