The in-house RAG engine (which replaced piragi) reads/writes a `content`
column and a `created_at` column on every chunks_<index_type> table and
provisions them at runtime via CREATE TABLE IF NOT EXISTS. On databases that
already carried the piragi-era tables (column `text`, no `created_at`) that
DDL is a silent no-op, so the engine never reshapes them and every
ingest/search/list fails with `column "content" ... does not exist`.
Migration 030 ALTERs each existing chunk table in place — renames
text -> content and adds created_at — preserving the non-rebuildable agent
knowledge (journals, decisions, errors, learnings, reviews, conversations)
that a docs reindex cannot regenerate. It guards on actual column presence,
so it is idempotent and safe on piragi-shaped, already-correct, or absent
tables (e.g. chunks_code).
Adds a guard test pinning the migration's table list to the IndexType enum so
a new index type cannot silently escape the schema alignment.
