feat: verify death certificate issuing authority and accepted forms (#34)

Verifies death certificate issuing authority (Bureau de l'etat civil) and accepted forms (certified_copy, copy) from Guichet.lu source pages. Upgrades verification_status to structured-from-source. Excellent research-based contribution by @HirenGajjar.

Author: HirenGajjar

data/document_requirements/lu/death-certificate.yaml

@@ -11,13 +11,14 @@ jurisdiction:
   municipality: null
 issuing_authority_id: null
 accepted_forms:
-  - unknown
+  - certified_copy
+  - copy
 source_ids:
   - source:lu:guichet:death-life-event
-verification_status: discovered
+verification_status: structured-from-source
 provenance:
   created_at: "2026-05-14"
   created_by: "clarvia-maintainers"
-  updated_at: null
-  updated_by: null
-notes: "Seed document requirement. Accepted forms and issuing authority must be verified before publication."
+  updated_at: "2026-05-23"
+  updated_by: "HirenGajjar"
+notes: "Issuing authority is the civil registrar's office (Bureau de l'état civil) of the communal administration in the commune where the death occurred — institution record not yet in data/institutions/lu/, to be created. Accepted forms verified from Guichet: certified_copy (extracts issued as standard) and copy (additional copies available on request)."