docs(timeline): register timeline domain in package tables and diagrams

Add timeline/ to the root and backend package tables, TimelineEvent to the
domain-model entity tables, TimelineEvent/EventType/Zeitstrahl to the
glossary, a new l3-backend-timeline C4 component diagram, and the
timeline_events table + two join tables (with their CHECKs and cascade FKs)
to the db-orm and db-relationships ER diagrams. Bumps the db-orm snapshot to
V77.

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

docs/architecture/db/db-relationships.puml

@@ -6,6 +6,7 @@
 ' precision/attribution fields); no new FK relationships, so this diagram is unchanged.
 ' Note: V76 swaps persons.birth_year/death_year for birth_date/death_date +
 ' precision columns; columns only, no new FK relationships, diagram unchanged.
+' Note: V77 adds the timeline_events table + two join tables (Timeline package below).
 
 hide circle
 skinparam linetype ortho
@@ -71,6 +72,13 @@ package "Supporting" {
   entity journey_items
 }
 
+' ── Timeline (Zeitstrahl) ──
+package "Timeline" {
+  entity timeline_events
+  entity timeline_event_persons
+  entity timeline_event_documents
+}
+
 ' Auth relationships
 app_users_groups }o--|| app_users : app_user_id
 app_users_groups }o--|| user_groups : group_id
@@ -136,4 +144,11 @@ journey_items }o--o| documents : document_id (ON DELETE SET NULL)
 note right of journey_items : partial UNIQUE (geschichte_id, document_id)\nWHERE document_id IS NOT NULL (V74)
 note right of geschichten : CHECK length(body) <= 4000\nfor type = JOURNEY (V75)
 
+' Timeline relationships (V77)
+timeline_event_persons }o--|| timeline_events : timeline_event_id (ON DELETE CASCADE)
+timeline_event_persons }o--|| persons : person_id (ON DELETE CASCADE)
+timeline_event_documents }o--|| timeline_events : timeline_event_id (ON DELETE CASCADE)
+timeline_event_documents }o--|| documents : document_id (ON DELETE CASCADE)
+note right of timeline_events : CHECK event_date_end non-null IFF RANGE\nCHECK date_precision <> 'UNKNOWN' (V77)
+
 @enduml