feat(wireless+ports): RF Health panels + physical per-port clients (v0.16.1-beta)

Wireless RF Health (fleet Wireless page + per-AP Radios tab):
- Channel usage map across 2.4/5/6 GHz with co-channel overlap; operating
  channel resolved live from /interface/wifi/monitor on the wifi package
  (auto-channel radios report no frequency in /print).
- AP deployment density: client RSSI distribution on the -90..-30 dBm scale
  with a coverage-gap warning.
- AP radio TX retries histogram (0%->35%+) with band selector, derived from
  per-client CCQ (new wireless_radio_quality InfluxDB series).
- WiFi connectivity success funnel (Association/Auth/DHCP) derived from logs.

Per-port connected clients (Ports tab):
- New card lists clients physically connected to a selected port (host/MAC/
  IP/VLAN/connection time, linked to client pages).
- Distinguishes physical clients from the raw MAC table: uplink/trunk ports
  are auto-detected (topology neighbor, multi-VLAN MAC spread, or high MAC
  count) and show an uplink explainer + "view MAC table" disclosure instead
  of every reachable MAC.
- Added clients.first_seen ("connected since"); set once, preserved across polls.

frontend/src/services/api.ts

@@ -225,6 +225,8 @@ export const devicesApi = {
   reboot: (id: number) => api.post<{ message: string }>(`/devices/${id}/reboot`),
   getPortMonitor: (id: number, name: string) =>
     api.get<PortMonitorData>(`/devices/${id}/ports/${encodeURIComponent(name)}/monitor`),
+  getPortClients: (id: number, name: string, all = false) =>
+    api.get<import('../types').PortClientsResult>(`/devices/${id}/ports/${encodeURIComponent(name)}/clients`, { params: { all: all || undefined } }),
   createBond: (id: number, data: {
     name: string; mode: string; slaves: string[];
     lacp_rate?: string; transmit_hash_policy?: string; mtu?: number; min_links?: number;
@@ -721,6 +723,16 @@ export const wirelessApi = {
   runAPScan:         (apId: number) => api.post(`/wireless/${apId}/ap-scan`),
   getAPScanHistory:  (apId: number, limit = 5) =>
     api.get(`/wireless/${apId}/ap-scan-history`, { params: { limit } }),
+
+  // RF Health (fleet-wide, or scoped to one AP via deviceId)
+  getChannelUsage: (deviceId?: number) =>
+    api.get<import('../types').RfChannelRow[]>('/wireless/rf/channels', { params: { deviceId } }),
+  getClientSignals: (deviceId?: number) =>
+    api.get<import('../types').RfSignalRow[]>('/wireless/rf/signals', { params: { deviceId } }),
+  getTxQuality: (deviceId?: number, range = '6h') =>
+    api.get<import('../types').RfTxQualityRow[]>('/wireless/rf/tx-quality', { params: { deviceId, range } }),
+  getConnectivity: (deviceId?: number, range = '24h') =>
+    api.get<import('../types').RfConnectivity>('/wireless/rf/connectivity', { params: { deviceId, range } }),
 };
 
 // ─── Network Services ─────────────────────────────────────────────────────────