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/en.json

@@ -751,5 +751,44 @@
 	"audit_action_comment_added": "commented:",
 	"audit_action_mention_created": "mentioned you in",
 
-	"dropzone_release": "Release to upload"
+	"dropzone_release": "Release to upload",
+
+	"chronik_page_title": "Chronicle",
+	"chronik_for_you_caption": "For you",
+	"chronik_for_you_count": "{count} new",
+	"chronik_mark_read_aria": "Mark as read",
+	"chronik_mark_all_read": "Mark all read",
+	"chronik_inbox_zero_title": "No new mentions",
+	"chronik_inbox_zero_link": "See older mentions →",
+	"chronik_filter_label": "Filter activity",
+	"chronik_filter_all": "All",
+	"chronik_filter_for_you": "For you",
+	"chronik_filter_uploaded": "Uploaded",
+	"chronik_filter_transcription": "Transcription",
+	"chronik_filter_comments": "Comments",
+	"chronik_day_today": "Today",
+	"chronik_day_yesterday": "Yesterday",
+	"chronik_day_this_week": "This week",
+	"chronik_day_older": "Older",
+	"chronik_singleton_text_saved": "{actor} transcribed a block in {doc}",
+	"chronik_rollup_text_saved": "{actor} transcribed {count} blocks in {doc}",
+	"chronik_singleton_uploaded": "{actor} uploaded {doc}",
+	"chronik_rollup_uploaded": "{actor} uploaded {count} documents",
+	"chronik_singleton_reviewed": "{actor} reviewed a block in {doc}",
+	"chronik_rollup_reviewed": "{actor} reviewed {count} blocks in {doc}",
+	"chronik_singleton_annotated": "{actor} annotated {doc}",
+	"chronik_rollup_annotated": "{actor} annotated {doc} {count}×",
+	"chronik_comment_added": "{actor} commented on {doc}",
+	"chronik_mention_created": "{actor} mentioned you in {doc}",
+	"chronik_reply_received": "{actor} replied to you in {doc}",
+	"chronik_empty_first_run_title": "Nothing has happened yet",
+	"chronik_empty_first_run_body": "As soon as someone in the family uploads or transcribes a document, the activity will show up here.",
+	"chronik_empty_filter_title": "Nothing in this view",
+	"chronik_empty_filter_body": "There are no entries for this filter.",
+	"chronik_error_title": "The chronicle could not be loaded.",
+	"chronik_error_retry": "Try again",
+	"chronik_load_more": "Load more",
+	"chronik_loading": "Loading …",
+	"chronik_load_more_announcement": "{count} more entries loaded",
+	"chronik_view_all": "Open chronicle →"
 }