chore(web): remove dead 'approval' case in ActivityTimeline icon map

The approval entry type was removed from ActivityEntry upstream; this
case/import were unreachable leftovers after merging that change in.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

web/src/lib/components/ActivityTimeline.svelte

@@ -8,7 +8,6 @@
   import SparklesIcon from '@lucide/svelte/icons/sparkles'
   import HelpCircleIcon from '@lucide/svelte/icons/help-circle'
   import FlagIcon from '@lucide/svelte/icons/flag'
-  import ShieldIcon from '@lucide/svelte/icons/shield'
   import ChevronDownIcon from '@lucide/svelte/icons/chevron-down'
   import ChevronRightIcon from '@lucide/svelte/icons/chevron-right'
 
@@ -30,7 +29,6 @@
       case 'knowledge': return SparklesIcon
       case 'complete': return FlagIcon
       case 'question': return HelpCircleIcon
-      case 'approval': return ShieldIcon
       default: return null
     }
   }