Add presence detection, person/vehicle AI detection, health monitoring

Task 1 — Presence: ping family phones, derive household state
(EMPTY/KIDS_HOME/ADULTS_HOME/ALL_HOME), configurable departure delay,
per-member roles, auto-arm actions via MQTT.

Task 2 — Detection: MobileNet-SSD v2 via OpenCV DNN for person/vehicle
classification. Vehicle color/size fingerprinting for known car matching.
Zone-based filtering per camera. Model download script.

Task 3 — Health: periodic disk/MQTT/subsystem checks, auto-prune oldest
non-starred recordings on disk pressure, daily digest builder.

126 tests passing.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

scripts/download_model.sh

@@ -0,0 +1,23 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+MODEL_DIR="${1:-/var/vigilar/models}"
+mkdir -p "$MODEL_DIR"
+
+PB_URL="https://raw.githubusercontent.com/opencv/opencv_extra/master/testdata/dnn/ssd_mobilenet_v2_coco_2018_03_29.pb"
+PBTXT_URL="https://raw.githubusercontent.com/opencv/opencv_extra/master/testdata/dnn/ssd_mobilenet_v2_coco_2018_03_29.pbtxt"
+
+echo "Downloading MobileNet-SSD v2 model..."
+if command -v curl &>/dev/null; then
+    curl -fSL -o "$MODEL_DIR/mobilenet_ssd_v2.pb" "$PB_URL"
+    curl -fSL -o "$MODEL_DIR/mobilenet_ssd_v2.pbtxt" "$PBTXT_URL"
+elif command -v wget &>/dev/null; then
+    wget -q -O "$MODEL_DIR/mobilenet_ssd_v2.pb" "$PB_URL"
+    wget -q -O "$MODEL_DIR/mobilenet_ssd_v2.pbtxt" "$PBTXT_URL"
+else
+    echo "ERROR: curl or wget required"
+    exit 1
+fi
+
+echo "Model downloaded to $MODEL_DIR"
+ls -lh "$MODEL_DIR"/mobilenet_ssd_v2.*