PgBouncer transaction-mode poolers can silently swallow ALTER TABLE
statements: the SQL doesn't error, but the column never gets created.
The migration system increments the schema version counter anyway, so
gbrain thinks it's on the latest version but the actual table is missing
columns. This caused production embed failures when the embed handler
tried to INSERT into columns that didn't exist.
Add verifySchema() that runs after all migrations complete:
1. Parses CREATE TABLE + ALTER TABLE ADD COLUMN from schema-embedded.ts
2. Queries information_schema.columns for actual DB state
3. Diffs expected vs actual columns
4. Self-heals missing columns via ALTER TABLE ADD COLUMN IF NOT EXISTS
5. Throws with actionable diagnostics if self-heal fails
Called from PostgresEngine.initSchema() after runMigrations().
PGLite skipped (in-process, no PgBouncer).
Co-authored-by: root <root@localhost>
