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>

backend/src/services/BackupService.ts

@@ -25,7 +25,7 @@ export class BackupService {
     }
   }
 
-  async createBackup(device: BackupDevice, notes?: string): Promise<number> {
+  async createBackup(device: BackupDevice, notes?: string, type: string = 'manual'): Promise<number> {
     const sshUser = device.ssh_username || device.api_username;
     const sshPass = device.ssh_password_encrypted
       ? decrypt(device.ssh_password_encrypted)
@@ -53,8 +53,8 @@ export class BackupService {
 
     const rows = await query<{ id: number }>(
       `INSERT INTO backups (device_id, filename, file_path, size_bytes, backup_type, notes)
-       VALUES ($1,$2,$3,$4,'manual',$5) RETURNING id`,
-      [device.id, filename, filePath, stats.size, notes || null]
+       VALUES ($1,$2,$3,$4,$5,$6) RETURNING id`,
+      [device.id, filename, filePath, stats.size, type, notes || null]
     );
 
     return rows[0].id;