Correct alarm data findings from byte tests

The alarm station byte is shared and follows the current radio station, so
remove the per-alarm control. Remove the FM sound option, as writing it just
turns on the radio mode. Record how the MCU treats each DP127 byte.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

CLAUDE.md

@@ -56,7 +56,13 @@ From Tuya's definition for a sibling product (tuya-local issue #3821). See the R
 - A knock during a ring snoozes it. DP130 then stays ON. Outside an alarm it returns to OFF at once.
 - DP127 writes are ignored while an alarm is snoozed.
 - A mode without light sets brightness to 0, and a light mode with brightness 0 falls back to no light, so the firmware sets a level when choosing a light mode.
-- Alarm radio stations were reset to 1 while no stations were saved.
+- Byte tests on DP127 with Alarm 4 off: time, days, ring duration, volume, sunrise and (in light modes) brightness are stored as written, with no range check, so the controls must limit them. The time's high byte keeps only its low 4 bits.
+- Byte 5 is bits: 0 = light, 1 = radio. Above 3 is ignored.
+- Byte 6: writing 8 or more turns on the radio bit and sets the sound to 1. It's locked at 1 in radio modes.
+- Byte 8 isn't per alarm. Every DP127 write sets all 4 to the current radio station, so there's no per-alarm station control.
+- Byte 10 is forced to 0 without the light bit, and writing 0 clears the light bit.
+- Byte 11: above 1 becomes 1.
+- What byte 4 actually does to ring length isn't confirmed. A test ring wasn't observed stopping.
 - Radio Volume and station writes are ignored with the radio off. With it on, both work, and the station stays selected after turning it off.
 - Keep `default_transition_length` at 0. A transition sends about 50 MCU writes a second.
 - LibreTiny before v1.14.0 can hang after a software restart or OTA until powered off for about 30 seconds (LibreTiny issue #396). The config pins v1.14.0. Drop the pin once ESPHome defaults to it or newer.