Polygres SDK 0.3.0

Added

• Added project.rows.validate(), insert(), upsert(), and ignore() for
  single-row Runtime writes with typed results and stable validation errors.
• Added explicit pgContext reconciliation to row writes, including completed,
  pending, and partial-failure outcomes backed by durable operations.
• Added PolygresAmbiguousWriteError for write outcomes that cannot be proven.

Changed

• Row mutations are sent exactly once. Automatic transport and status retries
  are disabled unless an exact Context-backed idempotency replay is requested.