feat(timeline): implement assembleDerivedEvents() with TDD (REQ-001–REQ-016)

Adds RelationshipService dependency to TimelineEventService and implements:
- assembleDerivedEvents() — public @Transactional(readOnly=true) orchestrator
- buildBirthEvents() — Person.birthDate → BIRTH events with precision pass-through
- buildDeathEvents() — Person.deathDate → DEATH events with precision pass-through
- buildMarriageEvents() — SPOUSE_OF edges → MARRIAGE events, dedup on row id

Synthetic prefixed ids (birth:/death:/marriage:) are structurally non-UUID.
Null fromYear marriages are emitted with eventDate=null + precision=UNKNOWN (REQ-006).
Non-family-member persons excluded from birth/death; SPOUSE_OF edges always emit (REQ-013).

All 16 tests in DerivedEventsAssemblyTest pass.

Refs #776
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/src/main/java/org/raddatz/familienarchiv/timeline/TimelineEventService.java

@@ -10,6 +10,8 @@ import org.raddatz.familienarchiv.exception.DomainException;
 import org.raddatz.familienarchiv.exception.ErrorCode;
 import org.raddatz.familienarchiv.person.Person;
 import org.raddatz.familienarchiv.person.PersonService;
+import org.raddatz.familienarchiv.person.relationship.PersonRelationship;
+import org.raddatz.familienarchiv.person.relationship.RelationshipService;
 import org.raddatz.familienarchiv.timeline.TimelineEventView.DocumentRef;
 import org.raddatz.familienarchiv.timeline.TimelineEventView.PersonView;
 
@@ -40,6 +42,7 @@ public class TimelineEventService {
     private final TimelineEventRepository events;
     private final PersonService personService;
     private final DocumentService documentService;
+    private final RelationshipService relationshipService;
 
     @Transactional
     public TimelineEventView create(TimelineEventRequest request, UUID actorId) {
@@ -229,6 +232,91 @@ public class TimelineEventService {
         return resolved;
     }
 
+    // --- derived event assembly ---
+
+    /**
+     * Assembles derived life-events (Geburt/Tod/Heirat) from curated Person and
+     * PersonRelationship data. Computed on read, never persisted.
+     *
+     * <p>Derived events are computed, never persisted, and cannot be mutated via the events API
+     * (enforced in #5). Ids produced by this method are structurally non-UUID
+     * ({@code birth:*}, {@code death:*}, {@code marriage:*}) and MUST be rejected by any
+     * write endpoint — enforced and tested in #5. Callers outside the #5 endpoint must
+     * independently enforce {@code READ_ALL} authorization before invoking this method
+     * (see ADR-043).
+     */
+    @Transactional(readOnly = true)
+    public List<TimelineEntryDTO> assembleDerivedEvents() {
+        List<Person> persons = personService.findAllFamilyMembers();
+        List<PersonRelationship> spouseEdges = relationshipService.findAllSpouseEdges();
+
+        List<TimelineEntryDTO> result = new ArrayList<>();
+        result.addAll(buildBirthEvents(persons));
+        result.addAll(buildDeathEvents(persons));
+        result.addAll(buildMarriageEvents(spouseEdges));
+
+        log.debug("Assembled {} derived events for {} persons", result.size(), persons.size());
+        return result;
+    }
+
+    private List<TimelineEntryDTO> buildBirthEvents(List<Person> persons) {
+        return persons.stream()
+                .filter(p -> p.getBirthDate() != null)
+                .map(p -> new TimelineEntryDTO(
+                        "birth:" + p.getId(),
+                        EventType.PERSONAL,
+                        p.getBirthDate(),
+                        p.getBirthDatePrecision(),
+                        true,
+                        DerivedEventType.BIRTH,
+                        p.getDisplayName(),
+                        null))
+                .toList();
+    }
+
+    private List<TimelineEntryDTO> buildDeathEvents(List<Person> persons) {
+        return persons.stream()
+                .filter(p -> p.getDeathDate() != null)
+                .map(p -> new TimelineEntryDTO(
+                        "death:" + p.getId(),
+                        EventType.PERSONAL,
+                        p.getDeathDate(),
+                        p.getDeathDatePrecision(),
+                        true,
+                        DerivedEventType.DEATH,
+                        p.getDisplayName(),
+                        null))
+                .toList();
+    }
+
+    private List<TimelineEntryDTO> buildMarriageEvents(List<PersonRelationship> spouseEdges) {
+        // DB constraint unique_spouse_pair (V55) is the authoritative enforcement;
+        // in-memory dedup on relationship row id is a defensive assertion.
+        Set<UUID> seen = new HashSet<>();
+        List<TimelineEntryDTO> result = new ArrayList<>();
+        for (PersonRelationship r : spouseEdges) {
+            if (seen.add(r.getId())) {
+                // JOIN FETCH in findAllSpouseEdges() guarantees person/relatedPerson are loaded
+                LocalDate eventDate = r.getFromYear() != null
+                        ? LocalDate.of(r.getFromYear(), 1, 1)
+                        : null;
+                DatePrecision precision = r.getFromYear() != null
+                        ? DatePrecision.YEAR
+                        : DatePrecision.UNKNOWN;
+                result.add(new TimelineEntryDTO(
+                        "marriage:" + r.getId(),
+                        EventType.PERSONAL,
+                        eventDate,
+                        precision,
+                        true,
+                        DerivedEventType.MARRIAGE,
+                        r.getPerson().getDisplayName(),
+                        r.getRelatedPerson().getDisplayName()));
+            }
+        }
+        return result;
+    }
+
     // --- view assembly (explicit allow-list; never the raw entity) ---
 
     private TimelineEventView toView(TimelineEvent event) {