docs: document the local: bool parameter across bake and resolution APIs

[bkfunk]

Summary

The local: bool flag threads through several entry points but has no doc comment anywhere:

• LibraryLoader::load_ref
• ResolutionResult::query
• bake_part_from_multipart_document
• bake_part_from_document

A reader at any one of those sites can't tell whether the flag has consistent semantics across them, or that the bake-time value silently has to match the resolution-time value. Callers (including in-tree tools and downstream consumers) tend to pass `false` by convention rather than understanding.

Change

Adds doc comments at the four sites explaining:

• `local = true`: this is a user-supplied / working-directory part. Sub-part references resolve against local entries first, then fall back to the stock library.
• `local = false`: this is a stock library part. Sub-part references resolve against library entries only.
• The bake-time value must match the value passed at resolution time; mismatches are not validated and may produce parts with missing or incorrect sub-geometry.

No code changes — only doc comments.

Test plan

• `cargo check -p ldraw -p ldraw-ir` passes
• `cargo doc -p ldraw -p ldraw-ir --no-deps` produces no intra-doc-link warnings

[Copilot]

Pull request overview

This PR improves API documentation by clearly defining the semantics of the local: bool flag across library loading, resolution lookup, and part baking entry points, including the requirement that the bake-time and resolution-time local values must match to avoid incorrect sub-part resolution.

Changes:

• Documented local: bool semantics on LibraryLoader::load_ref.
• Documented lookup behavior and the meaning of the returned bool on ResolutionResult::query.
• Documented local: bool semantics (and mismatch hazard) for bake_part_from_multipart_document and referenced it from bake_part_from_document.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
ldraw/src/library.rs	Adds rustdoc clarifying local resolution/search behavior for load_ref and ResolutionResult::query (including meaning of the returned bool).
ir/src/part.rs	Adds rustdoc explaining how local affects sub-part resolution during baking and that it must match the value used during dependency resolution.

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