Replace MQTT output with direct InfluxDB writes

Polls now cover meter 1, battery 1 and storage control blocks,
plus inverter event registers for off-grid detection (vendor
event bit 0). Register layout validated by probing a
SE10K-RWB48BFN4 with fw 0004.0025.0011; battery and storage
floats are word-swapped on this device.

Failed Influx writes spool to disk and replay on the next
success (Influx reached over WAN). Modbus blocks that fail to
read are skipped for that cycle; the flaky gateway must not
kill the daemon. Battery lifetime counters at 0xE176/0xE17A
hang the device and are never read.

BREAKING CHANGE: config.yaml 'mqtt:' section replaced by
'influx:', Home Assistant discovery removed.

README.md

@@ -13,6 +13,43 @@ cp config.yaml-dist /etc/solaredge_modbus_mqtt/config.yaml
 docker run --detach --name=solaredge_modbus_mqtt --restart=always --volume=/etc/solaredge_modbus_mqtt/config.yaml:/app/config.yaml marijnkoesen/solaredge_modbus_mqtt:latest
 ```
 
+### Configuration
+
+```yaml
+modbus:
+    host: 192.168.178.28     # inverter (SunSpec over Modbus TCP)
+    port: 1502
+    timeout: 1
+    unit: 1
+
+influx:
+    url: http://influx.example.com:8086
+    db: solaredge
+    user: ~                   # optional basic-auth user with WRITE on the db
+    pass: ~
+    measurement: solaredge
+
+poll_interval: 3
+```
+
+The daemon polls the inverter and writes one line-protocol point per cycle directly
+to InfluxDB. If InfluxDB is unreachable, points are spooled to `spool.txt` and
+replayed on the next successful write (capped at 20000 lines). Mount a volume for
+`/app/spool.txt` if backlog across container restarts matters.
+
+`model` and `serialnumber` are written as tags; everything else as fields.
+
+### Off-grid / fail-over
+
+- `offgrid` — boolean, true while the inverter runs islanded (off-grid) — vendor event bit
+- `error_code` — inverter vendor error bitmask (0 = none), LCD-style codes
+- `storage_control_mode_text` — e.g. `Backup Only`, `Maximize Self Consumption`
+- `battery1_*` — SOE/SOH, power, voltage, temperatures, status of battery 1
+
+Register addresses were validated by probing a SE10K-RWB48BFN4 (fw 0004.0025.0011)
+with one battery and one meter. Blocks that fail to read (flaky gateway) are
+skipped for that cycle; the fields are simply absent from the point.
+
 
 ### Uninstall