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>

README.md

@@ -140,13 +140,13 @@ Copy `server-example.yaml` to the server and add `wifi_ssid`, `wifi_password`, `
 
 Tuya's data model for this family was posted in [tuya-local issue #3821](https://github.com/make-all/tuya-local/issues/3821) for the sibling product `rslo8vqc1xjtaoy9`. It matches what this unit reports, and it replaces the older notes below where they differ.
 
-- **DP127** is 48 bytes on the unit tested here: 12 bytes per alarm, 4 alarms. Logs cut it off at 16 bytes, which likely explains the older 16-byte notes. Bytes: 0 enabled; 1-2 minutes since midnight; 3 repeat days (bit 0 = Monday, 0 = one time); 4 ring duration; 5 mode (0 sound, 1 sound + light, 2 radio, 3 radio + light); 6 sound; 7 volume; 8 radio station; 9 sunrise minutes; 10 brightness after sunrise; 11 snooze (0 allowed, 1 not).
+- **DP127** is 48 bytes on the unit tested here: 12 bytes per alarm, 4 alarms. Logs cut it off at 16 bytes, which likely explains the older 16-byte notes. Bytes: 0 enabled; 1-2 minutes since midnight; 3 repeat days (bit 0 = Monday, 0 = one time); 4 ring duration; 5 mode (bit 0 light, bit 1 radio); 6 sound 0-7; 7 volume; 8 current radio station, shared by all alarms; 9 sunrise minutes; 10 brightness after sunrise; 11 snooze (0 allowed, 1 not). The older "8 = FM" sound is really the MCU turning on the radio bit.
 - **DP128** is 10 bytes: 0 unused; 1 mode, as above; 2 sound 1-4; 3 volume; 4 sound duration; 5 radio station; 6 radio duration; 7 start brightness; 8 sunset duration; 9 snooze. Bytes 4, 6 and 8 should match.
 - **DP107** is stations found by a scan, then the current station. **DP126** starts (1) or ends (0) a channel search.
 - **DP117** and **DP132** are enums on this unit, so values count from 0. DP132 runs cycle, red, orange, yellow, green, cyan, blue, purple.
 - **DP125** is online time synchronization. **DP130** is snooze.
 
-Observed behaviour on this unit: a mode without light sets brightness to 0, and a light mode with brightness 0 falls back to no light. Alarm stations were reset to 1 while no stations had been scanned. DP127 writes are ignored while an alarm is snoozed. DP130 stays on after snoozing a ringing alarm and returns to off at once otherwise. Default light transitions flood the MCU with writes, so keep them at 0.
+Observed behaviour on this unit: a mode without light sets brightness to 0, and a light mode with brightness 0 falls back to no light. Every DP127 write sets byte 8 of all four alarms to the current radio station. Most other bytes are stored without any range check. DP127 writes are ignored while an alarm is snoozed. DP130 stays on after snoozing a ringing alarm and returns to off at once otherwise. Default light transitions flood the MCU with writes, so keep them at 0.
 
 ## DP127 alarm structure