feat: add Bureau de l'état civil institution, death certificate source, and link issuing authority

[HirenGajjar]

Closes #37

Follows up on PR #34 where issuing_authority_id was left null pending creation of the institution record. This PR closes that loop with 3 files: 1 new source, 1 new institution, 1 updated document requirement.

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Files changed

1. data/sources/lu/guichet-death-certificate.yaml — new file

A distinct source record for the dedicated Guichet death certificate page, separate from the general death life event page already in the repo.

• id: source:lu:guichet:death-certificate
• url: https://guichet.public.lu/en/citoyens/justice/certificats-copies-actes-casier-judicaire/certificats-copies-actes/acte-deces.html
• languages: en, fr, de (page has all three versions)
• Follows exact pattern of guichet-death-life-event.yaml

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2. data/institutions/lu/bureau-etat-civil.yaml — new file

Institution record for the civil registrar's office (Bureau de l'état civil) of the communal administration.

Source evidence:

"When a person dies, the death must be declared to the communal administration in the commune where the death occurred. For this reason, only the commune in question is able to issue a copy of the death certificate."
"The office of the civil registrar establishes the death certificate on the basis of the report issued by the doctor."

Schema compliance: Read schemas/v0.1/institution.schema.json carefully before writing. The schema has additionalProperties: false — no name_fr or name_de fields are permitted. name is a single string only. function is a free-text string, not an enum.

Design note: The Bureau de l'état civil exists within every communal administration in Luxembourg. This record represents the institution type, not any specific commune's office. This is documented in notes.

• official_site: the Guichet death certificate page — the most authoritative reference available, as the institution has no single national website
• languages: [fr, de, lb] — Luxembourg's three official languages
• verification_status: structured-from-source

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3. data/document_requirements/lu/death-certificate.yaml — updated

• issuing_authority_id: null → institution:lu:bureau-etat-civil
• source_ids: added source:lu:guichet:death-certificate
• provenance.updated_at: 2026-05-25
• notes: updated to reflect completed link

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Source evidence

Page: https://guichet.public.lu/en/citoyens/justice/certificats-copies-actes-casier-judicaire/certificats-copies-actes/acte-deces.html
Section: "How to proceed / Submitting the application"

"When a person dies, the death must be declared to the communal administration in the commune where the death occurred. For this reason, only the commune in question is able to issue a copy of the death certificate."
"The office of the civil registrar establishes the death certificate on the basis of the report issued by the doctor."

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Verified

• python3 scripts/validate.py — passes (10 data files, up from 8)
• Trailing newlines present on all 3 files
• git status — exactly 2 new files + 1 modified, nothing else touched
• Creation order: source → institution → document requirement (dependency order)

[TommiLindfors]

Merged! This is a milestone @HirenGajjar - your first multi-file PR, and it's flawless.

A few things that stood out:

• You caught that the institution schema has additionalProperties: false and doesn't allow name_fr/name_de. Reading the schema before writing is exactly the right workflow.
• The design note about Bureau de l'etat civil representing the institution type rather than a specific commune's office is important and well-documented.
• Creating files in dependency order (source → institution → document requirement) shows you understand how the data model connects.

Seven merged PRs. You're now an outside collaborator with write access and you're operating at maintainer quality. The about page issue (workflow-web #29) is waiting if you want to switch back to the web repo.