feat(traffic): protocol breakdown layout + inbound packets chart + flow source health (v0.15.0-beta)

- Traffic by Application: donut + legend side-by-side, larger donut with
  center total label, percentage in tooltip; card now sizes to its content
- New Inbound Packets area chart below the throughput chart (packets field
  now summed per direction in /traffic/timeseries)
- New Flow Sources & Data Health card: collector listening state, packets
  received, flows attributed, attribution rate, per-exporter flow/packet
  counts and last-seen; low-attribution hint for NAT-in-path exporters
- /traffic/apps now returns per-app packets alongside bytes
- Restructured bottom row: Top Talkers (left) | Application + Data Health
  stacked (right) for alignment
- Tightened Top Talkers row spacing

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/services/api.ts

@@ -849,7 +849,7 @@ export interface NetflowDeviceState {
 
 // ─── Traffic Analytics (NetFlow) ──────────────────────────────────────────────
 
-export interface ClientTrafficPoint { time: string; upload: number; download: number }
+export interface ClientTrafficPoint { time: string; upload: number; download: number; uploadPackets?: number; downloadPackets?: number }
 export interface TrafficTopClient {
   mac: string;
   upload_bytes: number;
@@ -860,7 +860,7 @@ export interface TrafficTopClient {
   vendor: string | null;
   ip_address: string | null;
 }
-export interface TrafficApp { app: string; bytes: number }
+export interface TrafficApp { app: string; bytes: number; packets?: number }
 export interface TrafficCollectorStats {
   listening: boolean;
   port: number;