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/models/device.py

@@ -0,0 +1,37 @@
+"""Device model."""
+from datetime import datetime, UTC
+from ..extensions import db
+
+
+class Device(db.Model):
+    """Discovered BLE/WiFi device."""
+    __tablename__ = 'devices'
+
+    id: db.Mapped[int] = db.mapped_column(primary_key=True)
+    mac: db.Mapped[str] = db.mapped_column(db.String(17), unique=True, index=True)
+    device_type: db.Mapped[str] = db.mapped_column(db.String(8))  # 'ble' or 'wifi'
+    vendor: db.Mapped[str | None] = db.mapped_column(db.String(64), nullable=True)
+    name: db.Mapped[str | None] = db.mapped_column(db.String(64), nullable=True)
+    first_seen: db.Mapped[datetime] = db.mapped_column(default=lambda: datetime.now(UTC))
+    last_seen: db.Mapped[datetime] = db.mapped_column(default=lambda: datetime.now(UTC))
+
+    # BLE-specific fields
+    company_id: db.Mapped[int | None] = db.mapped_column(nullable=True)
+    tx_power: db.Mapped[int | None] = db.mapped_column(nullable=True)
+
+    # Relationships
+    sightings = db.relationship('Sighting', back_populates='device', lazy='dynamic')
+    probes = db.relationship('Probe', back_populates='device', lazy='dynamic')
+
+    def to_dict(self):
+        return {
+            'id': self.id,
+            'mac': self.mac,
+            'type': self.device_type,
+            'vendor': self.vendor,
+            'name': self.name,
+            'first_seen': self.first_seen.isoformat(),
+            'last_seen': self.last_seen.isoformat(),
+            'company_id': self.company_id,
+            'tx_power': self.tx_power,
+        }