Add Samsung EHS (Eco Heating System) heat pump support

Adds a device registry for the TP1X_DA_AC_EHS board family: separate
zone1 (space heating/cooling) and dhw (domestic hot water) loops.
zone1 is exposed as power switch + mode select + current/target
temperature sensor/number -- it's a leaving-water-temperature
setpoint, not a thermostat, so no HA platform fits it better. dhw
gets a composite water_heater entity, using the same
primary-resource-plus-sibling-reads shape climate.py already uses
for the AC (PR #247 review feedback: "Having water heaters
automatically leverage the right platform would be pretty cool!").
The unit's away mode is a device-wide switch, not the water_heater
AWAY_MODE feature -- /option/outgoing/vs/0 has no dhw-scoped sibling
and covers zone1 too, so presenting it on the DHW card would
misstate its scope.

Operation modes (Eco/Std/Force/Power) map onto HA's own standard
water_heater states, the same mapping HA core's smartthings
integration uses for this exact Samsung capability over the cloud
API. Device codes are matched case-insensitively on the read side.
The DHW entity takes a catalog name ("Hot water") rather than the
bare device name -- unlike the AC's climate card, it is one loop of
a two-loop device.

Both temperature ranges fall back as a pair: a resource reporting a
minimum but no maximum yields no range at all rather than mixing a
device bound with an invented default, matching climate._range().
Increment fallbacks test for None instead of using `or`, so a
genuine 0 survives.

set_temperature honours the optional operation_mode HA's
water_heater service schema forwards, setting the mode (and powering
the loop on) before the setpoint, the same way climate's
set_temperature handles hvac_mode.

Entity names are translated into Czech and Dutch following each
file's existing terminology conventions.

Verified against a real TP1X_DA_AC_EHS_01001_0000 diagnostics dump
(firmware AEH-WW-TP1-22-AE6000_17260402); golden-regression fixture
and full test coverage included.

README.md

@@ -137,7 +137,7 @@ custom_components/localthings/
   diagnostics.py           Redacted diagnostics download (device state + coverage metadata)
   const.py                 Domain, config keys, probe ports
   entity.py                Base entity wiring capability registry -> HA entity
-  sensor.py / binary_sensor.py / switch.py / number.py / select.py / button.py / time.py / fan.py / climate.py
+  sensor.py / binary_sensor.py / switch.py / number.py / select.py / button.py / time.py / fan.py / climate.py / water_heater.py
                             One module per HA platform
   catalog.py               Reads the shipped translation catalog (which keys/states exist)
   translations/            Config-flow copy + entity name/state translations, one file per