Fix DOCX tables inside SDT content controls not being parsed

[aaarif796]

Summary

Fix parsing of DOCX tables contained within Structured Document Tags (SDT/content controls).

Root Cause

The SDT handler processed only paragraph elements (w:p) from w:sdtContent and ignored table elements (w:tbl).

As a result, tables embedded inside SDT content controls were flattened into plain text during DOCX conversion, causing Markdown export to lose table structure.

Fix

Handle table elements contained within w:sdtContent and route them through _handle_tables() while preserving existing paragraph handling.

Validation

• Reproduced issue using the DOCX attached in issue Table is not extracted correctly in DOCX #3655.
• Verified that tables inside SDT blocks are now parsed into TableItems.
• Added a regression test covering tables embedded in SDT content controls.
• Verified existing SDT-related tests continue to pass.

Before

Tables inside SDT blocks were flattened into text and exported as paragraphs.

After

Tables inside SDT blocks are correctly parsed and exported as Markdown tables.

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[PeterStaar-IBM]

@aaarif796 Can you tell me how your fix adds compared to #3657

[codecov]

Codecov Report

❌ Patch coverage is 54.54545% with 5 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
docling/backend/msword_backend.py	54.54%	5 Missing ⚠️

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[PeterStaar-IBM]

superseded by #3657