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/package-lock.json

@@ -1,12 +1,12 @@
 {
   "name": "mikrotik-manager-frontend",
-  "version": "0.14.1-beta",
+  "version": "0.15.0-beta",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "mikrotik-manager-frontend",
-      "version": "0.14.1-beta",
+      "version": "0.15.0-beta",
       "dependencies": {
         "@tanstack/react-query": "^5.17.1",
         "@types/leaflet": "^1.9.21",