feat(chronik): add ADR-003 + Paraglide keys for /chronik page (de/en/es)

- docs/adr/003-chronik-unified-activity-feed.md: records the session-rollup
  decision (LAG + 120-min gap), the dedupe deletion, the single-endpoint
  composition, and the German-URL convention.
- frontend/messages/{de,en,es}.json: adds chronik_* keys for page title,
  Für-dich box, filter pills, day headers, singleton/rollup verb variants
  per kind, empty states, error card, Mehr-laden pagination, and the Bell
  footer link retarget.

No pluralization via ICU match — separate singleton/rollup keys per verb,
per the Felix discussion (comment #3573).

Part of #285.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/messages/de.json

@@ -751,5 +751,44 @@
 	"audit_action_comment_added": "hat kommentiert:",
 	"audit_action_mention_created": "hat dich erwähnt in",
 
-	"dropzone_release": "Loslassen zum Hochladen"
+	"dropzone_release": "Loslassen zum Hochladen",
+
+	"chronik_page_title": "Chronik",
+	"chronik_for_you_caption": "Für dich",
+	"chronik_for_you_count": "{count} neu",
+	"chronik_mark_read_aria": "Als gelesen markieren",
+	"chronik_mark_all_read": "Alle gelesen",
+	"chronik_inbox_zero_title": "Keine neuen Erwähnungen",
+	"chronik_inbox_zero_link": "Ältere Erwähnungen ansehen →",
+	"chronik_filter_label": "Aktivitäten filtern",
+	"chronik_filter_all": "Alle",
+	"chronik_filter_for_you": "Für dich",
+	"chronik_filter_uploaded": "Hochgeladen",
+	"chronik_filter_transcription": "Transkription",
+	"chronik_filter_comments": "Kommentare",
+	"chronik_day_today": "Heute",
+	"chronik_day_yesterday": "Gestern",
+	"chronik_day_this_week": "Diese Woche",
+	"chronik_day_older": "Älter",
+	"chronik_singleton_text_saved": "{actor} transkribierte einen Block in {doc}",
+	"chronik_rollup_text_saved": "{actor} transkribierte {count} Blöcke in {doc}",
+	"chronik_singleton_uploaded": "{actor} lud {doc} hoch",
+	"chronik_rollup_uploaded": "{actor} lud {count} Dokumente hoch",
+	"chronik_singleton_reviewed": "{actor} überprüfte einen Block in {doc}",
+	"chronik_rollup_reviewed": "{actor} überprüfte {count} Blöcke in {doc}",
+	"chronik_singleton_annotated": "{actor} annotierte {doc}",
+	"chronik_rollup_annotated": "{actor} annotierte {doc} {count}×",
+	"chronik_comment_added": "{actor} kommentierte {doc}",
+	"chronik_mention_created": "{actor} erwähnte dich in {doc}",
+	"chronik_reply_received": "{actor} antwortete dir in {doc}",
+	"chronik_empty_first_run_title": "Noch nichts geschehen",
+	"chronik_empty_first_run_body": "Sobald jemand aus der Familie Dokumente hochlädt oder transkribiert, erscheint hier die Aktivität.",
+	"chronik_empty_filter_title": "Nichts in dieser Ansicht",
+	"chronik_empty_filter_body": "In diesem Filter gibt es keine Einträge.",
+	"chronik_error_title": "Die Chronik konnte nicht geladen werden.",
+	"chronik_error_retry": "Erneut versuchen",
+	"chronik_load_more": "Mehr laden",
+	"chronik_loading": "Lädt …",
+	"chronik_load_more_announcement": "{count} weitere Einträge geladen",
+	"chronik_view_all": "Zur Chronik →"
 }