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/models/__init__.py

@@ -13,6 +13,7 @@ from app.models.paper_trade import PaperTrade
 from app.models.regime_snapshot import RegimeSnapshot
 from app.models.benchmark_price import BenchmarkPrice
 from app.models.signal_context_snapshot import SignalContextSnapshot
+from app.models.system_event import SystemEvent
 
 __all__ = [
     "Ticker",
@@ -32,4 +33,5 @@ __all__ = [
     "RegimeSnapshot",
     "BenchmarkPrice",
     "SignalContextSnapshot",
+    "SystemEvent",
 ]

app/models/system_event.py

@@ -0,0 +1,37 @@
+"""Operational system events (warnings/errors) for the admin UI and top-nav badge."""
+
+from datetime import datetime
+
+from sqlalchemy import DateTime, Index, String, Text
+from sqlalchemy.orm import Mapped, mapped_column
+
+from app.database import Base
+
+
+class SystemEvent(Base):
+    """Durable warning/error record (jobs, ingestion, pipelines).
+
+    ``acknowledged_at`` is set when a user dismisses the nav badge / clears
+    events — history still shows in Admin → Jobs for the retention window.
+    """
+
+    __tablename__ = "system_events"
+    __table_args__ = (
+        Index("ix_system_events_created_at", "created_at"),
+        Index("ix_system_events_ack_created", "acknowledged_at", "created_at"),
+        Index("ix_system_events_dedup_created", "dedup_key", "created_at"),
+    )
+
+    id: Mapped[int] = mapped_column(primary_key=True)
+    severity: Mapped[str] = mapped_column(String(16), nullable=False)  # warning | error
+    source: Mapped[str] = mapped_column(String(64), nullable=False)
+    code: Mapped[str] = mapped_column(String(64), nullable=False)
+    message: Mapped[str] = mapped_column(Text, nullable=False)
+    symbol: Mapped[str | None] = mapped_column(String(20), nullable=True)
+    dedup_key: Mapped[str | None] = mapped_column(String(200), nullable=True)
+    created_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), default=datetime.utcnow, nullable=False
+    )
+    acknowledged_at: Mapped[datetime | None] = mapped_column(
+        DateTime(timezone=True), nullable=True
+    )