feat(podcast): enrich episodes with episode and youtube frontmatter

Add `episode:` and `youtube:` to the 220 modern (Podbean-hosted) episodes of
The PowerShell Podcast via a one-time local pass (Workstream 2).

- episode: parsed from the podcast_url filename; 217 set, 3 Summit/bar specials
  left blank. The eight earliest episodes encode the number as a single leading
  digit glued to a random Podbean suffix (episode_363s8e is ep 3, not 363), so
  they are pinned by chronology rather than greedy parsing.
- youtube: the episode's own video id, taken only from high-confidence in-body
  links (the canonical "...on YouTube: <url>" line, explicit "video version
  here" framings, and youtube.com/live links). 159 set; resource links to other
  videos are deliberately ignored so a miss degrades to a blank, not a wrong
  embed. The remaining blanks need the YouTube playlist (separate follow-up).
- guid is intentionally not written: the feed is truncated to its 10 most recent
  items (eps 226-235) and the archive tops out at 220, so no existing file is in
  the feed window. guid starts being recorded by the ongoing-sync Action (WS4).

Additions-only, idempotent, bodies byte-identical. hugo --gc --minify passes.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Q2NJsYE8nUKKHD25jXiHV1

Author: HeyItsGilbert