feat: implement Story 2.4 — Dashboard Activity Feed with review fixes

Add role-scoped activity feed to the dashboard showing the 20 most recent
workspace events. Owners/Managers see all activity (declarations, clients,
team changes); Workers see only their assigned declarations. Includes
French descriptions, relative timestamps, responsive layout (desktop
sidebar, tablet inline, mobile collapsible), and 7 passing Pest tests.

Review fixes applied: batch-load declarations/clients/users to eliminate
N+1 queries, consistent soft-delete handling in URL resolution, French
grammar singular/plural fix, missing icon map entry, and corrected tablet
breakpoint per spec.

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

_bmad-output/implementation-artifacts/sprint-status.yaml

@@ -34,7 +34,7 @@
 # - Dev moves story to 'review', then runs code-review (fresh context, different LLM recommended)
 
 generated: 2026-03-11
-last_updated: 2026-03-20T12:00:00
+last_updated: 2026-03-22T00:00:00
 project: "l'ami fiduciaire"
 project_key: NOKEY
 tracking_system: file-system
@@ -65,7 +65,7 @@ development_status:
   2-1-owner-manager-command-center-dashboard: done
   2-2-priority-alerts-panel: done
   2-3-worker-scoped-dashboard: review
-  2-4-dashboard-activity-feed: backlog
+  2-4-dashboard-activity-feed: done
   epic-2-retrospective: optional
 
   # Epic 3: Collaboration, Nudge System & Notifications