i18n(briefwechsel): DistributionBar reads text + aria-label via Paraglide

Drops the hardcoded German strings ("Briefverteilung in diesem Zeitraum",
"{n} von {name}") and routes every visible + assistive-tech string
through dist_bar_aria and dist_bar_segment message keys. An English
or Spanish user now sees "from" / "de" instead of "von" both on
screen and in the aria-label their screen reader announces.

Refs #305
Fixes @leonievoss i18n concern from PR review

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

frontend/messages/de.json

@@ -165,6 +165,8 @@
 	"conv_hero_divider": "oder",
 	"conv_empty_recent_label": "Zuletzt geöffnet",
 	"conv_no_party": "—",
+	"dist_bar_segment": "{count} von {name}",
+	"dist_bar_aria": "Briefverteilung in diesem Zeitraum: {outCount} von {senderName}, {inCount} von {receiverName}",
 	"admin_heading": "Admin Dashboard",
 	"admin_tab_users": "Benutzer",
 	"admin_tab_groups": "Gruppen",

frontend/messages/en.json

@@ -165,6 +165,8 @@
 	"conv_hero_divider": "or",
 	"conv_empty_recent_label": "Recently opened",
 	"conv_no_party": "—",
+	"dist_bar_segment": "{count} from {name}",
+	"dist_bar_aria": "Letter distribution in this period: {outCount} from {senderName}, {inCount} from {receiverName}",
 	"admin_heading": "Admin Dashboard",
 	"admin_tab_users": "Users",
 	"admin_tab_groups": "Groups",

frontend/messages/es.json

@@ -165,6 +165,8 @@
 	"conv_hero_divider": "o",
 	"conv_empty_recent_label": "Recientemente abiertos",
 	"conv_no_party": "—",
+	"dist_bar_segment": "{count} de {name}",
+	"dist_bar_aria": "Distribución de cartas en este período: {outCount} de {senderName}, {inCount} de {receiverName}",
 	"admin_heading": "Panel de administración",
 	"admin_tab_users": "Usuarios",
 	"admin_tab_groups": "Grupos",