Locks schema/code decisions for migrations 139-142 and downstream
sub-plans. Resolves open Risk questions from the absorption design spec.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
First of six sub-plans for the absorption. Six tasks: a discovery
audit that resolves the spec's Risk questions, four idempotent SQL
migrations (abs_sessions, podcast_feeds, media_libraries.kind,
audiobooks.enabled feature flag), and an empty-but-compiling
internal/audiobooks package scaffolded into cmd/silo. Lands as a
strict no-op for users (feature flag defaults to false).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
