feat: scheduled backups, availability tracking, PoE power metrics (v0.11.2 Beta)

P1 — Scheduled Backups
- BackupService.createBackup() now accepts a `type` param (manual/scheduled)
- PollerService: cronMatchesNow() parser + runScheduledBackups() + Redis 1h gate
- Settings page: backup schedule toggle + cron expression input with examples

P2 — Uptime/Availability Tracking
- DB: device_availability table (went_offline_at, came_back_online_at, duration_seconds)
- PollerService: inserts outage rows on offline detection, closes them on recovery
- GET /api/metrics/device/:id/availability?range=30d endpoint
- /api/metrics/summary now includes fleet 30-day uptime %
- DeviceDetailPage: 30-day availability card (uptime %, outage count, longest outage)
- DashboardPage HealthBar: Uptime 30d mini-stat

P3 — PoE Power Draw Metrics
- DeviceCollector.collectPoePower() queries /interface/ethernet/poe/monitor for switches
- Writes poe_power measurement to InfluxDB (tags: device_id, port; fields: watts, current_ma, voltage_v)
- GET /api/metrics/device/:id/poe endpoint (current per-port + 1h history)
- SwitchPortDiagram: amber watt badge on PoE-active ports
- HardwareTab: PoE budget section showing active ports and total watts

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/services/api.ts

@@ -8,6 +8,7 @@ import type {
   DeviceEvent,
   Backup,
   MetricsSummary,
+  DeviceAvailability,
   TimeSeriesPoint,
   TrafficPoint,
   ResourcePoint,
@@ -370,6 +371,10 @@ export const metricsApi = {
     }),
   deviceResources: (deviceId: number, range = '24h') =>
     api.get<ResourcePoint[]>(`/metrics/device/${deviceId}/resources`, { params: { range } }),
+  deviceAvailability: (deviceId: number, range = '30d') =>
+    api.get<DeviceAvailability>(`/metrics/device/${deviceId}/availability`, { params: { range } }),
+  devicePoe: (deviceId: number) =>
+    api.get<{ ports: { port: string; watts: number; current_ma: number; voltage_v: number }[]; totalWatts: number; history: { time: string; port: string; watts: number }[] }>(`/metrics/device/${deviceId}/poe`),
 };
 
 // ─── Topology ────────────────────────────────────────────────────────────────