feat: host inventory (agent.inventory), host detail page, UI columns

Store hardware/software snapshots on hosts; warn on hardware changes. Host card from Hosts list. Add agent version column to Events/Overview; rename Hosts table columns and sort by status.

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/src/api.ts

@@ -160,6 +160,7 @@ export interface EventSummary {
   host_id: number;
   hostname: string;
   display_name?: string | null;
+  product_version?: string | null;
   occurred_at: string;
   received_at: string;
   category: string;
@@ -187,6 +188,7 @@ export interface HostSummary {
   hostname: string;
   display_name: string | null;
   os_family: string;
+  os_version?: string | null;
   product: string;
   product_version: string | null;
   ipv4: string | null;
@@ -194,9 +196,24 @@ export interface HostSummary {
   event_count: number | null;
   last_heartbeat_at: string | null;
   last_daily_report_at: string | null;
+  last_inventory_at?: string | null;
   agent_status: "online" | "stale" | "unknown";
 }
 
+export interface HostDetail extends HostSummary {
+  agent_instance_id: string | null;
+  ipv6: string | null;
+  tags: string[] | null;
+  use_sac_mode: string | null;
+  inventory: Record<string, unknown> | null;
+  inventory_updated_at: string | null;
+  created_at: string | null;
+}
+
+export function fetchHost(id: number): Promise<HostDetail> {
+  return apiFetch<HostDetail>(`/api/v1/hosts/${id}`);
+}
+
 export interface HostListResponse {
   items: HostSummary[];
   total: number;