feat(web-ui): consume debounced scan.settled event; drop per-scanner lifecycle

Related #786

Spec 077 US4 (MCP-2207): forward the new security.scan_settled SSE event from the
system store as a mcpproxy:scan-settled window event, and have
useSecurityScannerStatus refresh its cached scan totals off that single settled
signal instead of tracking per-scanner lifecycle events.

## Changes
- stores/system.ts: add a security.scan_settled SSE listener that dispatches
  mcpproxy:scan-settled.
- composables/useSecurityScannerStatus.ts: register a module-scope
  mcpproxy:scan-settled listener that triggers a status refresh.

## Testing
- frontend vue-tsc --noEmit clean; vite build succeeds.

Related: Spec 077 (specs/077-scanner-simplification)

Author: Dumbris

frontend/src/composables/useSecurityScannerStatus.ts

@@ -17,6 +17,18 @@ const totalFindings = ref<number>(0)
 const totalScans = ref<number>(0)
 let inflight: Promise<void> | null = null
 
+// Spec 077 US4 (MCP-2207): the backend now collapses the per-scanner
+// scan_started/progress/completed/failed storm into a single debounced
+// `security.scan_settled` event per server per scan (forwarded by the system
+// store as `mcpproxy:scan-settled`). We consume that one settled signal to
+// refresh the cached scan totals, instead of tracking per-scanner lifecycle
+// events. Registered once at module scope so all consumers share it.
+if (typeof window !== 'undefined') {
+  window.addEventListener('mcpproxy:scan-settled', () => {
+    void refreshSecurityScannerStatus()
+  })
+}
+
 export async function refreshSecurityScannerStatus(): Promise<void> {
   if (inflight) {
     return inflight

frontend/src/stores/system.ts

@@ -185,6 +185,19 @@ export const useSystemStore = defineStore('system', () => {
       }
     })
 
+    // Spec 077 US4 (MCP-2207): a single debounced settled event per server per
+    // scan replaces the per-scanner scan_started/progress/completed/failed
+    // storm. Forward it so scan-status consumers can refresh once per scan.
+    es.addEventListener('security.scan_settled', (event) => {
+      try {
+        const data = JSON.parse(event.data)
+        const payload = data.payload || data
+        window.dispatchEvent(new CustomEvent('mcpproxy:scan-settled', { detail: payload }))
+      } catch (error) {
+        console.error('Failed to parse SSE security.scan_settled event:', error)
+      }
+    })
+
     // Listen for activity events (tool calls, policy decisions, etc.)
     es.addEventListener('activity.tool_call.started', (event) => {
       try {