feat: Dashboard MVP with summary API and UI

Add GET /api/v1/dashboards/summary (24h events, open problems,
hosts, severity breakdown, recent events) and Vue /dashboard page.

backend/app/api/v1/dashboards.py

@@ -0,0 +1,77 @@
+from datetime import datetime, timedelta, timezone
+
+from fastapi import APIRouter, Depends
+from pydantic import BaseModel
+from sqlalchemy import func, select
+from sqlalchemy.orm import Session, joinedload
+
+from app.auth.jwt_auth import get_current_user
+from app.database import get_db
+from app.models import Event, Host, Problem
+from app.schemas.list_models import EventSummary
+
+router = APIRouter(prefix="/dashboards", tags=["dashboards"])
+
+
+class DashboardSummary(BaseModel):
+    events_last_24h: int
+    hosts_total: int
+    problems_open: int
+    severity_24h: dict[str, int]
+    recent_events: list[EventSummary]
+
+
+@router.get("/summary", response_model=DashboardSummary)
+def dashboard_summary(
+    db: Session = Depends(get_db),
+    _user: str = Depends(get_current_user),
+) -> DashboardSummary:
+    since = datetime.now(timezone.utc) - timedelta(hours=24)
+
+    events_24h = db.scalar(
+        select(func.count()).select_from(Event).where(Event.received_at >= since)
+    ) or 0
+    hosts_total = db.scalar(select(func.count()).select_from(Host)) or 0
+    problems_open = (
+        db.scalar(select(func.count()).select_from(Problem).where(Problem.status == "open")) or 0
+    )
+
+    severity_rows = db.execute(
+        select(Event.severity, func.count())
+        .where(Event.received_at >= since)
+        .group_by(Event.severity)
+    ).all()
+    severity_24h = {row[0]: row[1] for row in severity_rows}
+
+    recent = db.scalars(
+        select(Event)
+        .join(Host)
+        .options(joinedload(Event.host))
+        .order_by(Event.received_at.desc())
+        .limit(8)
+    ).all()
+
+    recent_events = [
+        EventSummary(
+            id=e.id,
+            event_id=e.event_id,
+            host_id=e.host_id,
+            hostname=e.host.hostname,
+            occurred_at=e.occurred_at,
+            received_at=e.received_at,
+            category=e.category,
+            type=e.type,
+            severity=e.severity,
+            title=e.title,
+            summary=e.summary,
+        )
+        for e in recent
+    ]
+
+    return DashboardSummary(
+        events_last_24h=events_24h,
+        hosts_total=hosts_total,
+        problems_open=problems_open,
+        severity_24h=severity_24h,
+        recent_events=recent_events,
+    )