Add official Luxembourg source objects for death declaration

[TommiLindfors]

Scope

Add structured Source objects for Luxembourg's official death-declaration process. Cover the Guichet.lu life-event pages, the relevant Code Civil articles, and any official Ministry of Justice references.

Source links

• https://guichet.public.lu/en/citoyens/famille/deces/deces/declaration-deces.html
• https://guichet.public.lu/fr/citoyens/famille/deces/deces/declaration-deces.html

Acceptance criteria

• Source objects added to data/sources/lu/
• Source URL included
• Access date included
• Language included
• Jurisdiction set to lu
• Validation passes
• Review status assigned (discovered or structured-from-source)

Trust level

maintainer-only

[TommiLindfors]

Closing as completed. Source records for death declaration exist: guichet-death-life-event.yaml and guichet-death-certificate.yaml, both now source-checked (PR #39).