Drop composite isPrimary on NotifiedThreshold model
Lucid's BaseModel doesn't genuinely support composite primary keys — marking
both subject_uri and threshold as isPrimary is cosmetic and makes reload,
$primaryKeyValue, and .find() behave surprisingly. Keep only subject_uri as
the Lucid-level primary key; the SQLite composite PK (enforced by the
migration) still guarantees uniqueness.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>