feat(election): audit log UI with server-side filter, pagination, entity-aware actions

- New ElectionAuditLogComponent: timeline view, expandable JSON details
- Server-side filtering: entityType, action, full-text search (350ms debounce)
- Pagination bar with page size selector (10/20/50 per page)
- Action dropdown filtered by selected entity (CANDIDATE shows only
  candidate actions, NOMINATION shows nomination actions, etc.)
- Entity change resets action filter automatically
- election.service.ts: getAuditLog() sends query params to backend
- Audit Log button added to every election card in dashboard
- Route: /election/:electionId/audit-log

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

src/app/election/components/election-dashboard/election-dashboard.component.html

@@ -132,6 +132,9 @@
                 <mat-icon>bar_chart</mat-icon> Results
               </a>
             }
+            <a [routerLink]="['/election', election.id, 'audit-log']" class="btn-audit">
+              <mat-icon>history</mat-icon> Audit Log
+            </a>
           </div>
         </div>
       }