docs(timeline): add derived-event glossary entries and update C4 diagram

Add GLOSSARY.md entries for derived event, DerivedEventType, derivedType,
and assembleDerivedEvents() to cover the vocabulary introduced by #776.
Update l3-backend-timeline.puml: remove stale "planned, #775" labels,
add Rel from TimelineEventService to personDomain for assembleDerivedEvents
batch-fetch calls, document the on-read strategy in the component notes.

Refs #776
Co-Authored-By: claude-sonnet-4-6 <noreply@anthropic.com>

docs/GLOSSARY.md

@@ -168,7 +168,16 @@ _Not to be confused with a document item's optional note_ — a document item's
 
 **EventType** (`EventType`) `[user-facing]` — the kind of a `TimelineEvent`: `PERSONAL` (a family event, rendered with the family accent) or `HISTORICAL` (world/historical context, rendered with a muted world accent). The string value names are a stable frontend styling contract — renaming requires a coordinated frontend change (ADR-040).
 
-**Zeitstrahl** `[user-facing]` — the family timeline view, rendering curated `TimelineEvent`s (and, in later issues, derived life-events) chronologically. The milestone home of the `timeline` domain.
+**Zeitstrahl** `[user-facing]` — the family timeline view, rendering curated `TimelineEvent`s and derived life-events chronologically. The milestone home of the `timeline` domain.
+
+**derived event** — a timeline entry computed on-read from curated `Person` or `PersonRelationship` data, never persisted. Carried as a `TimelineEntryDTO` with `derived=true` and a non-null `DerivedEventType`. Three subtypes: Geburt (birth, from `Person.birthDate`), Tod (death, from `Person.deathDate`), Heirat (marriage, from a `SPOUSE_OF` `PersonRelationship` edge). Callers of `assembleDerivedEvents()` are responsible for enforcing `READ_ALL` authorization before invoking it (ADR-043).
+_Not to be confused with a `TimelineEvent`_ — a `TimelineEvent` is a curated record authored by a human and stored in `timeline_events`; a derived event is computed on-the-fly and never written to the database.
+
+**DerivedEventType** (`DerivedEventType`) `[internal]` — enum with three values: `BIRTH`, `DEATH`, `MARRIAGE`. Carried on `TimelineEntryDTO.derivedType`; `null` on curated-event entries exposed through the same DTO.
+
+**derivedType** (`TimelineEntryDTO.derivedType`) `[internal]` — the `DerivedEventType` field distinguishing a derived Geburt/Tod/Heirat event from a curated one. Always non-null on derived events; `null` on curated events.
+
+**assembleDerivedEvents()** (`TimelineEventService.assembleDerivedEvents()`) `[internal]` — the public `@Transactional(readOnly=true)` method that computes all derived events in one call: one batch fetch of family-member `Person`s via `PersonService.findAllFamilyMembers()` and one batch fetch of `SPOUSE_OF` edges via `RelationshipService.findAllSpouseEdges()`. Result is never persisted. Synthetic ids produced by this method (`birth:{uuid}`, `death:{uuid}`, `marriage:{uuid}`) are structurally non-UUID and must be rejected by any write endpoint. See ADR-043.
 
 **Notification** (`Notification`) — an in-app message delivered to an `AppUser`. No email or SMS delivery exists today. Delivered via Server-Sent Events (`SseEmitterRegistry`) and persisted in the `notifications` table.