feat(timeline): add TimelineEvent entity and repository

Curated timeline event mirroring Document's date block (eventDate /
precision / eventDateEnd) so events and letters share one rendering path.
Audit footprint deliberately diverges from Document: @Version optimistic
lock plus NOT NULL createdBy/updatedBy for the multi-curator edit flow.
precision reuses document.DatePrecision (imported, not duplicated) and
defaults to YEAR. ManyToMany persons/documents with explicit @JoinTable +
@BatchSize, matching Document's join conventions.

Repository is empty for now with a TODO marker for the issue-5 per-person
filter query.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

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

@@ -0,0 +1,129 @@
+package org.raddatz.familienarchiv.timeline;
+
+import jakarta.persistence.*;
+import lombok.*;
+import org.hibernate.annotations.BatchSize;
+import org.hibernate.annotations.CreationTimestamp;
+import org.hibernate.annotations.UpdateTimestamp;
+
+import io.swagger.v3.oas.annotations.media.Schema;
+
+import org.raddatz.familienarchiv.document.DatePrecision;
+import org.raddatz.familienarchiv.document.Document;
+import org.raddatz.familienarchiv.person.Person;
+
+import java.time.LocalDate;
+import java.time.LocalDateTime;
+import java.util.HashSet;
+import java.util.Set;
+import java.util.UUID;
+
+/**
+ * A curated event on the family timeline (Zeitstrahl). Unlike a {@link Document}, which is
+ * OCR-derived, a {@code TimelineEvent} is authored by curators — hence the optimistic-lock
+ * {@link #version} and the {@link #createdBy}/{@link #updatedBy} audit trail that
+ * {@code Document} lacks.
+ *
+ * <p>The date block ({@link #eventDate}, {@link #precision}, {@link #eventDateEnd}) mirrors
+ * {@code Document}'s so events and letters share one rendering path. The mirror applies to
+ * the date block only — the audit footprint deliberately diverges (see ADR-040).
+ */
+@Entity
+@Table(name = "timeline_events")
+@Data
+@NoArgsConstructor
+@AllArgsConstructor
+@Builder
+public class TimelineEvent {
+
+    @Id
+    @GeneratedValue(strategy = GenerationType.UUID)
+    @Schema(requiredMode = Schema.RequiredMode.REQUIRED)
+    private UUID id;
+
+    @Column(nullable = false)
+    @Schema(requiredMode = Schema.RequiredMode.REQUIRED)
+    private String title;
+
+    @Enumerated(EnumType.STRING)
+    @Column(nullable = false, length = 16)
+    @Schema(requiredMode = Schema.RequiredMode.REQUIRED)
+    private EventType type;
+
+    /** The most precise date known for the event. Always present — a curated event is never undated. */
+    @Column(name = "event_date", nullable = false)
+    @Schema(requiredMode = Schema.RequiredMode.REQUIRED)
+    private LocalDate eventDate;
+
+    /**
+     * Precision of {@link #eventDate}. Reuses {@code document.DatePrecision} (one rendering
+     * path; see ADR-025 / ADR-040). Every value except {@code UNKNOWN} is legal for a curated
+     * event — including {@code SEASON} ("Sommer 1914") and {@code APPROX} ("ca. 1914"). The DB
+     * CHECK forbids exactly {@code UNKNOWN}; do not narrow it further.
+     */
+    @Enumerated(EnumType.STRING)
+    @Column(name = "date_precision", nullable = false, length = 16)
+    @Builder.Default
+    @Schema(requiredMode = Schema.RequiredMode.REQUIRED)
+    private DatePrecision precision = DatePrecision.YEAR;
+
+    /** Range end — non-null <strong>iff</strong> {@link #precision} is {@code RANGE} (DB CHECK, both directions). */
+    @Column(name = "event_date_end")
+    private LocalDate eventDateEnd;
+
+    @Column(columnDefinition = "TEXT")
+    private String description;
+
+    /** People the event involves. */
+    @ManyToMany(fetch = FetchType.LAZY)
+    @JoinTable(name = "timeline_event_persons",
+            joinColumns = @JoinColumn(name = "timeline_event_id"),
+            inverseJoinColumns = @JoinColumn(name = "person_id"))
+    @BatchSize(size = 50)
+    @Builder.Default
+    private Set<Person> persons = new HashSet<>();
+
+    /** Optional supporting letters linked to the event. */
+    @ManyToMany(fetch = FetchType.LAZY)
+    @JoinTable(name = "timeline_event_documents",
+            joinColumns = @JoinColumn(name = "timeline_event_id"),
+            inverseJoinColumns = @JoinColumn(name = "document_id"))
+    @BatchSize(size = 50)
+    @Builder.Default
+    private Set<Document> documents = new HashSet<>();
+
+    /**
+     * UUID of the {@code AppUser} who created the event. Bare UUID, no FK to {@code app_users}
+     * (sidecar pattern — keeps {@code timeline} decoupled from {@code user}). Server-populated
+     * from the session principal; never accepted from client input (authorship-forgery vector,
+     * CWE-639 — see ADR-040).
+     */
+    @Column(name = "created_by", nullable = false)
+    private UUID createdBy;
+
+    @CreationTimestamp
+    private LocalDateTime createdAt;
+
+    /**
+     * UUID of the {@code AppUser} who last edited the event. Populated from the session
+     * principal in {@code TimelineEventService}; <strong>must be set before every
+     * {@code save()}</strong> — {@code @UpdateTimestamp} on {@link #updatedAt} does NOT set this
+     * automatically, so without an explicit set the timestamp advances while the "who" goes
+     * stale. Same forgery rationale as {@link #createdBy}.
+     */
+    @Column(name = "updated_by", nullable = false)
+    private UUID updatedBy;
+
+    @UpdateTimestamp
+    private LocalDateTime updatedAt;
+
+    /**
+     * Optimistic-lock version for the multi-curator edit flow (issue 3). Object {@code Long}
+     * (not primitive) so it is {@code null} before first persist; Hibernate sets {@code 0} on
+     * insert. A concurrent-write conflict must be translated to {@code DomainException.conflict}
+     * in the service layer (ADR-040) — otherwise it surfaces as HTTP 500 with Hibernate
+     * internals (CWE-209).
+     */
+    @Version
+    private Long version;
+}

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

@@ -0,0 +1,9 @@
+package org.raddatz.familienarchiv.timeline;
+
+import org.springframework.data.jpa.repository.JpaRepository;
+
+import java.util.UUID;
+
+public interface TimelineEventRepository extends JpaRepository<TimelineEvent, UUID> {
+    // TODO(issue 5): findByPersonsContaining(Person) needed for the per-person filter
+}