li3: add Lithionics Li3 house battery BMS -> Home Assistant MQTT

Publishes the RV's 12V LiFePO4 house battery to HA via MQTT discovery
(pack voltage, 4 cell voltages, current, SOC, BMS/battery temp, status).
Connects over the battery's BLE HM-10 UART module (service ffe0/char
ffe1, no pairing) using bleak; protocol reverse-engineered from the
com.lithionics.bms Android app's own BLE/parsing code.

Deliberately named li3/ and van-li3-battery, not battery/van-battery —
that name is reserved for the host's own AC/UPS power-supply monitor
(different hardware, unrelated concern).

Self-heals a bluetoothd discovery-state wedge (Discovering stuck "yes",
connects failing with le-connection-abort-by-local) that shows up after
repeated failed connects to this device on the Pi's onboard adapter: the
daemon retries scan/connect internally (MQTT session and HA entities
stay up across retries) and restarts bluetooth.service itself after 3
consecutive scan failures, rate-limited to once per 5 min.

README.md

@@ -143,6 +143,16 @@ This directory is the source of truth. The live system files live under `/etc`,
 The `hbc` binary itself (venv at `~/venvs/hbd`, symlink `~/bin/hbc`) is installed once via the
 heartbeat project's own installer — see §4. `deploy.sh` only starts the service once it exists.
 
+### `li3/` — RV house battery (BLE BMS → MQTT/HA)
+| file | → installs to | purpose |
+|---|---|---|
+| `van-li3-battery` | `/usr/local/sbin/van-li3-battery` | BLE→MQTT daemon (Python, bleak + paho-mqtt): reads the Lithionics Li3 BMS, publishes HA MQTT discovery + state |
+| `config.json.example` | → `/etc/van-li3/config.json` (seeded if absent) | BLE address, broker, MQTT topic/discovery **template**; real file is 0600, **not** in the repo |
+| `van-li3-battery.service` | `/etc/systemd/system/van-li3-battery.service` | `Restart=always` |
+
+Not to be confused with `power/van-battery` — that's the host's own AC/battery power
+supply (laptop UPS-style monitor), unrelated hardware and purpose.
+
 ### `ha/` — Home Assistant (native container)
 | file | → installs to | purpose |
 |---|---|---|
@@ -256,6 +266,31 @@ paho 2.x callback API.
 - Note: the broker holds an ancient *retained* message on this topic from a 2023
   OwnTracks device (tid `RV`, Winegard SSID); our publishes are not retained.
 
+### Li3 battery monitor (`van-li3-battery`)
+Publishes the RV's 12V LiFePO4 house battery (Lithionics Li3, BLE HM-10 UART module —
+service `ffe0`/char `ffe1`, no pairing) to Home Assistant as 10 sensor entities (pack
+voltage, 4 cell voltages, current, SOC, BMS/battery temperature, status) via MQTT
+discovery. Protocol (CSV telemetry lines after sending `$traceon`+`$info`) reverse-
+engineered from the `com.lithionics.bms` Android app's own BLE/parsing code — see the
+script's docstring for the full field layout.
+- Not the same battery as `power/van-battery` (host's own AC/UPS power supply) —
+  different hardware, different concern, deliberately different naming.
+- Broker credentials live only in `/etc/van-li3/config.json` (0600, seeded from
+  `li3/config.json.example` — edit after first deploy, same pattern as `van-gps`).
+- **Self-healing BLE**: scan/connect retries happen *inside* the running process (MQTT
+  session and HA entities stay up across them, no flapping) rather than relying on
+  systemd restarts. This Pi's onboard Bluetooth adapter (Cypress/CYW43) occasionally
+  wedges bluetoothd's discovery state after a run of failed connects to this specific
+  device (`Discovering` stays `yes` forever, every subsequent connect fails with
+  `le-connection-abort-by-local`) — after 3 consecutive scan failures the daemon
+  restarts `bluetooth.service` itself to clear it, rate-limited to once per 5 min so it
+  doesn't repeatedly disrupt the AP's other BLE gear (motion sensors, IR remote).
+- This BLE module accepts only **one central connection at a time** — while
+  `van-li3-battery` holds it, the Li3 phone app can't connect simultaneously.
+  `systemctl stop van-li3-battery` to free it up for the app.
+- Verify: `journalctl -u van-li3-battery -f` (look for `connected` / `published: {...}`),
+  or `mosquitto_sub -h localhost -u homeassistant -P <pw> -t van/li3_battery/state`.
+
 ### ZeroTier managed DNS
 - `wrede.pvt` resolves over ZeroTier when off the home LAN. Mechanism: `allowDNS=1` (prereq) + `zerotier-systemd-manager` writes `99-ztuga7c2kh.network`, networkd applies it to resolved.
 - Verify: `resolvectl status ztuga7c2kh` shows `DNS` scope + the two servers + `wrede.pvt`.