feat: Initial project scaffold

Flask API backend for ESP32 sensor fleet:
- App factory pattern with blueprints
- SQLAlchemy 2.x models (Sensor, Device, Sighting, Alert, Event, Probe)
- UDP collector for sensor data streams
- REST API endpoints for sensors, devices, alerts, events, probes, stats
- pytest setup with fixtures
- Containerfile for podman deployment
- Makefile for common tasks

src/esp32_web/api/alerts.py

@@ -0,0 +1,29 @@
+"""Alert endpoints."""
+from datetime import datetime, timedelta, UTC
+from flask import request
+from . import bp
+from ..models import Alert
+from ..extensions import db
+
+
+@bp.route('/alerts')
+def list_alerts():
+    """List alerts with filters."""
+    alert_type = request.args.get('type')
+    sensor_id = request.args.get('sensor_id', type=int)
+    hours = request.args.get('hours', 24, type=int)
+    limit = min(int(request.args.get('limit', 100)), 1000)
+    offset = int(request.args.get('offset', 0))
+
+    since = datetime.now(UTC) - timedelta(hours=hours)
+    query = db.select(Alert).where(Alert.timestamp >= since).order_by(Alert.timestamp.desc())
+
+    if alert_type:
+        query = query.where(Alert.alert_type == alert_type)
+    if sensor_id:
+        query = query.where(Alert.sensor_id == sensor_id)
+
+    query = query.limit(limit).offset(offset)
+    alerts = db.session.scalars(query).all()
+
+    return {'alerts': [a.to_dict() for a in alerts], 'limit': limit, 'offset': offset}