feat: Event archive management — Event model, migration, API, frontend page (Phase 8)

- Event ORM model with status/level enums, domain categories, review tracking
- Alembic migration e7f3a9b1c5d0 for events table
- Event crawler service with placeholder data (12 sample events)
- GET /api/v1/events with status/domain/search filtering and overdue_days
- EventArchivePage with filter toolbar (status, domain, search) and adaptive card grid
- Status badges, level badges, domain tags, overdue markers on event cards
- Loading/error/empty states, hover-to-honey card interaction

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

frontend/src/api/events.ts

@@ -0,0 +1,26 @@
+import client from './client'
+
+export interface EventItem {
+  id: string
+  title: string
+  level: 'A' | 'B' | 'C'
+  domain: string
+  status: 'active' | 'fading' | 'dissipating' | 'closed'
+  occurred_date: string
+  last_reviewed: string | null
+  no_new_info_count: number
+  next_review: string | null
+  overdue_days: number
+  created_at: string | null
+  updated_at: string | null
+}
+
+export interface EventsResponse {
+  events: EventItem[]
+}
+
+export const getEvents = (params?: {
+  status?: string
+  domain?: string
+  search?: string
+}) => client.get<EventsResponse>('/events', { params })