Start building out the podcast room

/podcasts is a standing page with a holding line on it. What it needs deciding:

• Where the audio files live. Vercel is the wrong home for large media, so this is a hosting question before it is an architecture one.
• Whether an episode is an entry with audio attached — kind: "episode" already exists in the schema — or something with its own shape.
• Whether the page becomes a section index like Model Behavior once there are episodes to list, rather than the standing page it is now.

Nothing should be built until there is a first episode to build around.