chore: add intake_screener role to WorkerRole + role_map + idp.toml

Issue #497 (closed) example referenced an intake_screener role that doesn't exist in WorkerRole. MR4 ships the 4 real roles (eligibility_worker, supervisor, analyst, jurisdiction_admin); this FU adds the 5th.

Scope:

• Add WorkerRole::IntakeScreener variant + Display impl.
• Extend role_slug_for_worker mapping.
• Add to Keycloak realm seed + rulesets/georgia/idp.toml.
• Decide which surfaces (worker dashboard / case detail) the role can reach.

Tracking origin: Stage 5 MR4 (#497 (closed)) descope. Refs &51.