feat(canopy-caps): provider registry — replace placeholder provider-001 strings with FK lookups

Source: canopy-seed-caps-wic-fixtures plan Potential Improvements.

CAPS authorizations currently reference provider IDs as opaque strings ("provider-001"). Once a CAPS provider registry exists (separate plan), replace string IDs with foreign keys to a real caps_providers table.

Acceptance: new caps_providers table + provider CRUD on canopy-caps; provider_authorizations.provider_id becomes UUID NOT NULL REFERENCES caps_providers; seeder populates a small provider catalogue.

Out of scope: provider self-service portal, provider credentialing.