feat(podcast): add guest names to authors field for 198 episodes

Wrote and ran scripts/update-podcast-authors.py to extract host and
guest names from 817 podcast episode files and populate the `authors`
frontmatter array, enabling the author taxonomy pages to list episodes
by participant. Extraction uses four strategies in priority order:
bio section headers, "Guest:" body lines, "Tonight's Guest:" title
pattern, and "with Name" title fallback. Also fixes a regex bug where
NOT_A_PERSON_RE lacked word boundaries on "Just", "Set", and "Get",
causing Justin Grote's episodes to be skipped.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FNNC3yU5uCsjfcts7GGVow

Author: claude