fix(xml-formatter): recover from malformed XML in tool call parsing

[francisjervis]

Summary

Add a recovery pass using clean_malformed_xml before failing, and return an empty list instead of raising on parse error.

Problem

When the LLM returns structurally malformed XML (mismatched tags, stray angle brackets inside field values, etc.), ET.fromstring raises ET.ParseError. This caused background AgendaManager._process_qa_pair tasks to die silently, leaving memory/subtopic-coverage state partially un-updated.

Changes (src/utils/llm/xml_formatter.py)

• Attempt 1: parse XML as-is (existing behaviour).
• Attempt 2: on ParseError, run clean_malformed_xml on the string and retry.
• Fallback: if both attempts fail, log the error and return [] so the calling interview continues unimpeded.