Stop surfacing '_OFF'-suffixed placeholder alarm codes (#166)

Samsung pre-populates /alarms/vs/0 with one row per supported alarm type,
each carrying a '<Name>_OFF' placeholder code (no 'Deleted' state at all)
when that alarm isn't firing. common._active_alarm_codes only ever
filtered on 'Deleted' state, so every device using this shared capability
(including the AC family) showed these inert placeholders --
'ErrorCode_OFF', 'FilterAlarm_OFF' -- as if they were live alarms.

Confirmed the '_OFF' suffix convention holds across every alarm code seen
in this repo's fixtures so far (ErrorCode_OFF, FilterAlarm_OFF, OV_E_OFF,
CT_E_OFF, WaterTankFull_OFF, AC_V_0002_OFF, all placeholders; DoorA_Opened,
FilterAlarm, SNSF_Reached, all genuinely active with no suffix) -- issue
#166's own dump has both a FilterAlarm_OFF placeholder and, on a second
unit, a live FilterAlarm/state=Created alert, which is what motivated
generalizing range_hood.py's existing (but narrower, ErrorCode_OFF-only)
special case into the shared helper instead of duplicating it further.

The other three points in #166 (filter-usage percentage vs. filterStatus
disagreement, an "air purification" config toggle the reporter says has no
physical effect, a "beep on/off" control) don't have a confirmed code fix:
the percentage math already matches the device's own filterUsage/
filterCapacity fields (filterStatus is a separate device-computed field we
already relay verbatim, not something we derive), the air-purify resource
is correctly wired to what the board reports and its absence from the
official app's own options list suggests an inert shared-board-profile stub
rather than an integration bug, and a "Beep volume" NumberDesc keyed off
the same Volume_100 option both dumps report already exists (0 mutes it).

tests/test_common_capabilities.py

@@ -184,6 +184,40 @@ class TestWmSetinfoFlags:
             },
         ]) == 'LE'
 
+    def test_off_suffixed_placeholder_codes_filtered(self):
+        """issue #166: Samsung pre-populates /alarms/vs/0 with one row per
+        supported alarm *type*, each carrying a '<Name>_OFF' placeholder
+        code (no 'Deleted' state at all) when that alarm isn't firing --
+        confirmed not just for 'ErrorCode_OFF' but also 'FilterAlarm_OFF'
+        on the same dump. These were previously shown as if they were
+        active alarms."""
+        assert common._active_alarm_codes([
+            {
+                'x.com.samsung.da.code': 'ErrorCode_OFF',
+                'x.com.samsung.da.triggeredTime': '2026-07-28T12:59:22',
+            },
+            {
+                'x.com.samsung.da.code': 'FilterAlarm_OFF',
+                'x.com.samsung.da.triggeredTime': '2026-07-28T12:59:22',
+            },
+        ]) == 'none'
+
+    def test_real_filter_alarm_not_off_suffixed_still_shown(self):
+        """issue #166's actual live filter alert: code 'FilterAlarm' (no
+        '_OFF' suffix), state 'Created' -- distinct from the 'FilterAlarm_OFF'
+        placeholder and must still surface."""
+        assert common._active_alarm_codes([
+            {
+                'x.com.samsung.da.code': 'ErrorCode_OFF',
+                'x.com.samsung.da.triggeredTime': '2026-07-28T12:59:22',
+            },
+            {
+                'x.com.samsung.da.code': 'FilterAlarm',
+                'x.com.samsung.da.state': 'Created',
+                'x.com.samsung.da.triggeredTime': '2026-07-28T12:59:22',
+            },
+        ]) == 'FilterAlarm'
+
 
 class TestKidsLockFallback:
     def test_generic_read_write(self):