feat: implement Phase 5 — Alerting & Monitoring

Backend:
- AlertEvaluationService: evaluates metrics against AlertRules after each heartbeat
  - Supports cpu_usage_percent and memory_usage_percent metric paths
  - Operators: >, >=, <, <=, ==
  - 15-minute dedup window to prevent alert spam
- AlertRulesController: full CRUD for alert rules (GET/POST/PUT/DELETE)
- AlertsController: list with acknowledged filter + POST acknowledge endpoint
- IRmmHubClient: added AlertTriggered push method
- Program.cs: AlertEvaluationService registered as Scoped

Frontend:
- AlertsPage: two-tab layout (active alerts + rules)
  - Alerts tab: severity badges, acknowledge button, all/unack/ack filter
  - Rules tab: condition display, enabled toggle, delete with confirm
  - Create rule modal with MetricPath/Operator/Threshold/Severity selects
- api/types.ts: AlertRule, AlertItem, CreateAlertRuleRequest types
- api/client.ts: alertRulesApi and alertsApi
- useAgentSignalR: handles AlertTriggered → invalidates alerts query
- App.tsx: Alerts nav item with Bell icon

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

Frontend/src/api/client.ts

@@ -6,6 +6,10 @@ import type {
   CreateTaskRequest,
   CreateTicketRequest,
   UpdateTicketRequest,
+  AlertRule,
+  AlertItem,
+  CreateAlertRuleRequest,
+  UpdateAlertRuleRequest,
 } from './types'
 
 const BASE_URL = '/api/v1'
@@ -48,3 +52,24 @@ export const ticketsApi = {
   update: (id: number, data: UpdateTicketRequest) =>
     request<Ticket>(`/tickets/${id}`, { method: 'PUT', body: JSON.stringify(data) }),
 }
+
+// Alert Rules
+export const alertRulesApi = {
+  list: () => request<AlertRule[]>('/alert-rules'),
+  create: (data: CreateAlertRuleRequest) =>
+    request<AlertRule>('/alert-rules', { method: 'POST', body: JSON.stringify(data) }),
+  update: (id: number, data: UpdateAlertRuleRequest) =>
+    request<AlertRule>(`/alert-rules/${id}`, { method: 'PUT', body: JSON.stringify(data) }),
+  delete: (id: number) =>
+    request<void>(`/alert-rules/${id}`, { method: 'DELETE' }),
+}
+
+// Alerts
+export const alertsApi = {
+  list: (acknowledged?: boolean) => {
+    const param = acknowledged !== undefined ? `?acknowledged=${acknowledged}` : ''
+    return request<AlertItem[]>(`/alerts${param}`)
+  },
+  acknowledge: (id: number) =>
+    request<{ id: number; acknowledged: boolean }>(`/alerts/${id}/acknowledge`, { method: 'POST' }),
+}

Frontend/src/api/types.ts

@@ -93,3 +93,42 @@ export interface UpdateTicketRequest {
   status?: TicketStatus
   priority?: TicketPriority
 }
+
+export interface AlertRule {
+  id: number
+  name: string
+  metricPath: string
+  operator: string
+  threshold: number
+  severity: AlertSeverity
+  enabled: boolean
+}
+
+export interface AlertItem {
+  id: number
+  message: string
+  severity: AlertSeverity
+  acknowledged: boolean
+  createdAt: string
+  agentId: string
+  agentHostname: string
+  ruleId: number
+  ruleName: string
+}
+
+export interface CreateAlertRuleRequest {
+  name: string
+  metricPath: string
+  operator: string
+  threshold: number
+  severity: AlertSeverity
+}
+
+export interface UpdateAlertRuleRequest {
+  name?: string
+  metricPath?: string
+  operator?: string
+  threshold?: number
+  severity?: AlertSeverity
+  enabled?: boolean
+}