Dialect-split: portable rollup queries on TTPMixin; bulk insert with
ON CONFLICT DO NOTHING / INSERT IGNORE in the per-dialect repos.
Confidence-floor (< 0.3) drop applied at mixin layer before the
dialect hook. BaseRepository now declares the six TTP methods abstract.
Tests in tests/web/db/test_ttp_repo.py flipped from pytest.fail stubs
to real dual-backend behavioral tests; tests/ttp/test_confidence.py
drop-below-floor xfail removed.
Empty NotImplementedError bodies; the SQL lands at E.3 implementation.
Mixin composed onto SQLModelRepository alongside the existing domain
mixins. Dialect-specific INSERT-OR-IGNORE syntax overrides land in
the per-backend subclasses at E.3 per the dual-DB-backend convention.
