Alert on genuinely new (never-seen-before) devices

New seen_macs table: permanent, insert-only, MAC-keyed record of the
first time each device was ever seen -- deliberately decoupled from
devices.first_seen (IP-keyed, would false-positive on every DHCP
lease change). Bootstrap-safe: first call seeds the baseline from
whatever's currently on the network without alerting on all 71+
existing devices at once. Verified locally: bootstrap call reports
nothing new, repeat calls with the same MACs report nothing new, one
genuinely new MAC gets reported exactly once.

Pushes a Home Assistant persistent_notification when a new MAC
appears (gated behind HOME_ASSISTANT_TOKEN + homeAssistant.url in
hosts.yaml -- missing config just means no push, detection still
runs). Also surfaced directly in the dashboard as a blue "new" badge
for anything first seen in the last 24h, independent of HA config.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

config/hosts.yaml

@@ -13,6 +13,13 @@ deepCheck:
   host: 192.168.1.103
   username: root
 
+# Push a persistent_notification to Home Assistant whenever a MAC address is
+# seen for the first time ever (not "unknown", genuinely new -- see
+# docs/device-discovery.md). Requires HOME_ASSISTANT_TOKEN in .env too; if
+# either is missing, detection still runs but nothing gets pushed.
+homeAssistant:
+  url: http://192.168.1.187:8123
+
 # Bare-metal boxes Proxmox can't see. Connects with the dedicated
 # `monitor` SSH key (see docs/ssh-collector-key-setup.md), read-only commands only.
 sshHosts: