v0.1.5 - PostgreSQL fix (upgrade if you use Postgres)

PostgreSQL users on 0.1.1-0.1.4 should upgrade: their catalog was empty.

• Fixed: PostgreSQL reflected nothing at all. 0.1.1 added an
  internal-schema filter for Oracle Autonomous Database and put public on
  the list, because PUBLIC is a pseudo-schema on Oracle. On PostgreSQL
  public is the user's entire database, so every schema was filtered out and
  Catalog.bootstrap() returned zero objects. Caught by running
  scripts/certify_dialect.py against a live PostgreSQL 16, which failed 7 of
  10 checks.
• Internal-schema detection now lives behind a per-dialect hook
  (schemagate.dialects.is_internal_schema) and applies only to the engine
  that defines it. A test asserts no cross-dialect list exists in
  introspect.py, because that is what caused this.
• PostgreSQL 16 re-certified live: certify script 10/10, plus the dialect
  and 260-object hostile suites.
• The OCI stack installs the driver matching your database URL instead of
  always Oracle, so create_adb = false with a PostgreSQL, SQL Server or MySQL
  URL now works rather than failing at import.
• Stack: shape_config for Flex shapes (A1.Flex is the other Always Free
  option and would 400 without it), a selectable availability domain for the
  "out of host capacity" case, GenAI policy scoped to the compartment instead
  of the tenancy, and preconditions that catch a missing password or database
  URL at plan time.