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>

backend/app/main.py

@@ -4,7 +4,7 @@ from fastapi import FastAPI
 from fastapi.middleware.cors import CORSMiddleware
 
 from app.database import engine, Base
-from app.api import auth, users, audit, dashboard, gateway, health, cron, keys, kanban
+from app.api import auth, users, audit, dashboard, gateway, health, cron, keys, kanban, events
 from app.middleware.audit import AuditMiddleware
 
 
@@ -39,6 +39,7 @@ app.include_router(gateway.router, prefix="/api/v1")
 app.include_router(health.router, prefix="/api/v1")
 app.include_router(cron.router, prefix="/api/v1")
 app.include_router(kanban.router, prefix="/api/v1")
+app.include_router(events.router, prefix="/api/v1")
 app.include_router(keys.router, prefix="/api/v1")