feat(timeline): add timeline i18n keys (de/en/es)

14 Paraglide keys for the /zeitstrahl view: nav link, heading, empty/undated/
gap/unknown-person chrome, letters count, strip expand, range aria, and the
layer/derived labels. The layer (Weltgeschehen/Familie) and derived (Geburt/
Tod/Heirat) labels carry the German term across all locales by design
(documented MVP decision). REQ-024.

Refs #779
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/messages/de.json

@@ -1032,6 +1032,20 @@
 	"bulk_edit_count_pill": "{count} werden bearbeitet",
 	"nav_stammbaum": "Stammbaum",
 	"nav_geschichten": "Geschichten",
+	"nav_zeitstrahl": "Zeitstrahl",
+	"timeline_heading": "Zeitstrahl",
+	"timeline_empty_state": "Noch keine Ereignisse.",
+	"timeline_undated_section": "Ohne Datum",
+	"timeline_unknown_person": "Unbekannt",
+	"timeline_gap_empty": "keine Einträge",
+	"timeline_letters_count": "{count} Briefe",
+	"timeline_strip_expand": "Briefe anzeigen",
+	"timeline_range_aria": "Zeitraum: {from} bis {to}",
+	"timeline_layer_world": "Weltgeschehen",
+	"timeline_layer_family": "Familie",
+	"timeline_derived_birth": "Geburt",
+	"timeline_derived_death": "Tod",
+	"timeline_derived_marriage": "Heirat",
 	"error_geschichte_not_found": "Die Geschichte wurde nicht gefunden.",
 	"error_journey_item_not_found": "Der Reise-Eintrag wurde nicht gefunden.",
 	"error_journey_item_position_conflict": "Die Reihenfolge wurde gerade von jemand anderem geändert – bitte laden Sie die Seite neu.",

frontend/messages/en.json

@@ -1032,6 +1032,20 @@
 	"bulk_edit_count_pill": "{count} will be edited",
 	"nav_stammbaum": "Family tree",
 	"nav_geschichten": "Stories",
+	"nav_zeitstrahl": "Timeline",
+	"timeline_heading": "Timeline",
+	"timeline_empty_state": "No events yet.",
+	"timeline_undated_section": "Without Date",
+	"timeline_unknown_person": "Unknown",
+	"timeline_gap_empty": "no entries",
+	"timeline_letters_count": "{count} letters",
+	"timeline_strip_expand": "Show letters",
+	"timeline_range_aria": "Period: {from} to {to}",
+	"timeline_layer_world": "Weltgeschehen",
+	"timeline_layer_family": "Familie",
+	"timeline_derived_birth": "Geburt",
+	"timeline_derived_death": "Tod",
+	"timeline_derived_marriage": "Heirat",
 	"error_geschichte_not_found": "The story was not found.",
 	"error_journey_item_not_found": "The journey item was not found.",
 	"error_journey_item_position_conflict": "The order was just changed by someone else — please reload the page.",

frontend/messages/es.json

@@ -1032,6 +1032,20 @@
 	"bulk_edit_count_pill": "Se editarán {count}",
 	"nav_stammbaum": "Árbol genealógico",
 	"nav_geschichten": "Historias",
+	"nav_zeitstrahl": "Línea de tiempo",
+	"timeline_heading": "Línea de tiempo",
+	"timeline_empty_state": "Aún no hay eventos.",
+	"timeline_undated_section": "Sin Fecha",
+	"timeline_unknown_person": "Desconocido",
+	"timeline_gap_empty": "sin entradas",
+	"timeline_letters_count": "{count} cartas",
+	"timeline_strip_expand": "Mostrar cartas",
+	"timeline_range_aria": "Período: {from} a {to}",
+	"timeline_layer_world": "Weltgeschehen",
+	"timeline_layer_family": "Familie",
+	"timeline_derived_birth": "Geburt",
+	"timeline_derived_death": "Tod",
+	"timeline_derived_marriage": "Heirat",
 	"error_geschichte_not_found": "No se encontró la historia.",
 	"error_journey_item_not_found": "No se encontró el elemento del viaje.",
 	"error_journey_item_position_conflict": "El orden fue cambiado por otra persona — por favor recargue la página.",