feat(podcasts): make podcasts always available + smarter mention matching

Changes:
- Podcasts source is now always available when yt-dlp is installed (same as
  YouTube). Previously required explicit opt-in via INCLUDE_SOURCES or
  --search=podcasts.
- Smarter mention matching: extract key terms from multi-word topics and
  use max count across terms. "Kanye West Bully album" now matches
  episodes mentioning "Kanye" 85 times (previously 0 due to exact phrase).
- SKILL.md: add podcast channel resolution to Step 0.55, include
  --podcast-channels in execution command, update ACTIVE_SOURCES_LIST.

Tested: Kanye West query now finds 5 podcast hits including hidden
mentions in off-topic episodes (Lost Civilizations, Mike WiLL Made-It).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

scripts/lib/pipeline.py

@@ -124,7 +124,10 @@ def available_sources(config: dict[str, Any], requested_sources: list[str] | Non
         available.append("pinterest")
     if env.is_xquik_available(config):
         available.append("xquik")
-    if podcast_yt.is_available() and ("podcasts" in include_sources or (requested_sources and "podcasts" in requested_sources)):
+    # Podcasts: available whenever yt-dlp is installed (same as YouTube).
+    # Opt-out only. The source returns empty when no channels are resolved,
+    # so there's no cost to having it available.
+    if podcast_yt.is_available():
         available.append("podcasts")
     return available