bug(tools): save_body_as_part opens a linked assembly and leaves it open #101

Symptom

After a successful save_body_as_part call, an extra Assem<N> document is
open in SolidWorks (unsaved, no path). Reproduced live during the PR #99
tutorial run — list_open_documents afterwards showed the source part plus an
Assem14 that the tool never mentions.

Cause

IFeatureManager::CreateSaveBodyFeature in
src/solidworks_mcp/adapters/solidworks/io.py save_body_as_part is called
as:

manager.CreateSaveBodyFeature(
    _variant_array(pythoncom.VT_DISPATCH, [match]),
    _variant_array(pythoncom.VT_BSTR, [target]),
    "",      # AssemblyName
    False,
    True,
)

SolidWorks' Save Bodies feature has a "Create assembly" option that is on by
default; one of the trailing args (or the empty AssemblyName being treated as
"auto") is triggering assembly creation. The standalone .sldprt is still
written correctly — this is just an unwanted side document.

Impact

Low — the file write (the tool's actual contract) works and is verified. But
the stray assembly:

• pollutes list_open_documents
• can confuse close_model (which acts on the active doc) in a cleanup loop
• is surprising: the tool's docstring says nothing about an assembly

Fix

Confirm the exact CreateSaveBodyFeature signature against sldworks.tlb on
the target install, pass the arg combination that suppresses assembly
creation, and if an assembly is unavoidable, either close it in the tool or
document it and return its name in the response.

Context

PR #99, tutorial docs/getting-started/tutorials/wave3-reference-geometry-and-drawings.md
("Save Bodies opens a linked assembly" note).