SMT v1.4.0

Added

• Public schema-evolution DDL API (#247) — schema.Renderer now
  exposes deterministic drops for schemas, tables, indexes, and named
  constraints; column add/drop/type/nullability/default changes; and table
  truncation. The public API returns ordered schema.Batch artifacts and
  keeps execution, retry, and transaction policy with the caller. Built-in
  capability reporting covers PostgreSQL, SQL Server, MySQL, SQLite, and
  ClickHouse; unsupported operations return
  *schema.UnsupportedFeatureError instead of silently degrading or proposing
  a rebuild. PostgreSQL supports the complete current surface and explicit
  cascade; SQL Server and MySQL support the non-cascade surface; SQLite and
  ClickHouse advertise only their supported subsets. MySQL/SQLite destructive
  batches carry same-connection cleanup semantics, SQL Server default
  replacement is an ordered same-connection batch, and SQLite sequence cleanup
  is explicitly best effort. EvolutionCapabilities is a companion extensible
  public capability surface, preserving existing exported Capabilities and
  Statement struct layouts. RendererVersion 19 → 20.

• Expression IR for DEFAULT / CHECK translation (#175) — new
  internal/expr package: a source default or CHECK predicate is parsed once
  into a small dialect-neutral tree (ParseDefault / ParseCheck), rendered
  to any of the three targets from that one parse (Render), and compared
  structurally (Equal). All three targets — not just PostgreSQL — now share
  one translation with equal coverage (now/UTC-now/uuid families,
  CONVERT(date, …)/::date casts, ISNULL ≡ COALESCE ≡ IFNULL,
  CONCAT ≡ ||, boolean 0/1 rewrites, IN lists, LIKE-bracket-class and
  regex forms, MySQL fsp-matched now-defaults) and one fail-closed invariant:
  an unparseable or unknown-function expression is rejected on every target
  instead of silently passed through.

• Snapshot-mode sync (#167) — smt sync --against snapshot diffs the
  current source schema against the latest stored snapshot, with scope
  filtering, object-kind gating, plan summary, unsupported-change refusal,
  deterministic ALTER rendering, and the same risk gates as live-target sync.

Changed

• Side-object AI review uses structured comparison ([#177]) — index,
  foreign-key, and check-constraint review now deterministically compares
  structured source metadata and generated DDL instead of asking a model to
  judge free text.
• Added a CI CRM fixture matrix covering all nine supported SQL Server,
  PostgreSQL, and MySQL source-to-target permutations.