Add system alerts log with nav badge and Admin Alerts tab.

Persist job and ingestion warnings/errors for 7 days, surface a dismissible top-nav badge, treat stale OHLCV as a warning (e.g. ticker renames), and show market bar age on the ticker freshness chip.

app/routers/admin.py

@@ -6,7 +6,7 @@ All endpoints require admin role.
 from fastapi import APIRouter, Depends, Query
 from sqlalchemy.ext.asyncio import AsyncSession
 
-from app.dependencies import get_db, require_admin
+from app.dependencies import get_db, require_access, require_admin
 from app.models.user import User
 from app.schemas.admin import (
     ActivationConfigUpdate,
@@ -29,6 +29,7 @@ from app.schemas.common import APIEnvelope
 from app.services import admin_service
 from app.services import alert_service
 from app.services import sentiment_provider_service
+from app.services import system_event_service
 from app.services import ticker_universe_service
 
 router = APIRouter(tags=["admin"])
@@ -403,3 +404,50 @@ async def toggle_job(
         status="success",
         data={"key": setting.key, "value": setting.value},
     )
+
+
+# ---------------------------------------------------------------------------
+# System events (operational warnings / errors)
+# ---------------------------------------------------------------------------
+
+@router.get("/admin/system-events", response_model=APIEnvelope)
+async def list_system_events(
+    days: int = Query(7, ge=1, le=30),
+    severity: str | None = Query(None, description="warning | error"),
+    unacknowledged_only: bool = Query(False),
+    _user: User = Depends(require_access),
+    db: AsyncSession = Depends(get_db),
+):
+    """List recent system events (default last 7 days)."""
+    rows = await system_event_service.list_events(
+        db,
+        days=days,
+        severity=severity,
+        unacknowledged_only=unacknowledged_only,
+    )
+    return APIEnvelope(
+        status="success",
+        data=[system_event_service.event_to_dict(r) for r in rows],
+    )
+
+
+@router.get("/admin/system-events/summary", response_model=APIEnvelope)
+async def system_events_summary(
+    days: int = Query(7, ge=1, le=30),
+    _user: User = Depends(require_access),
+    db: AsyncSession = Depends(get_db),
+):
+    """Badge counts for the top nav."""
+    data = await system_event_service.summary(db, days=days)
+    return APIEnvelope(status="success", data=data)
+
+
+@router.post("/admin/system-events/acknowledge", response_model=APIEnvelope)
+async def acknowledge_system_events(
+    days: int = Query(7, ge=1, le=30),
+    _user: User = Depends(require_access),
+    db: AsyncSession = Depends(get_db),
+):
+    """Dismiss unacknowledged events in the lookback window (clears the badge)."""
+    count = await system_event_service.acknowledge_all(db, days=days)
+    return APIEnvelope(status="success", data={"acknowledged": count})