Resolved: IS NULL/IS NOT NULL (#1), pg executor (#2), alias collision (#3).
New: Record DTS mismatch (#6), stock TS stack overflow (#7).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

…rows

Resolves flags.md #1 (SQLite inserts emitted NULL for missing values,
breaking NOT NULL DEFAULT columns). Instead of a per-dialect
missing-value placeholder:

- Columns no row provides are pruned from the INSERT column list, so
  the DB applies its own semantics natively — identity/rowid
  autoincrement, declared DEFAULT expressions, or NULL. This is what
  a hand-written INSERT would do, and needs no per-column metadata
  (column() keeps no runtime opts).
- Heterogeneous rows (column set in some rows but not others): PG
  keeps the per-gap DEFAULT keyword; SQLite has no per-row spelling
  for "use the default", so raise with a clear message rather than
  silently inserting NULL.
- Zero provided columns: `DEFAULT VALUES` for a single row; raise for
  multi-row (unspellable in both dialects).

The sqlite example's seed data mixed rows with and without `breed` —
now explicit `breed: null`, which is what the old behavior actually
did.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>