feat: upgrade FFE1 command to 34 bytes with control byte

Per 协议简述(3): Byte33 is now control instruction (0=IDLE, 1=scan,
2=treat), Byte34 is XOR checksum. Backward compat with 33-byte
read-back preserved. All command sites updated with correct control:
- auto-scan: control=0x01 (scan mode)
- treatment-setup: control=0x02 (treat mode)
- stopTreatment: control=0x00 (IDLE)

miniprogram/pages/auto-scan/auto-scan.js

@@ -67,7 +67,8 @@ Page({
       region_mask: 0x1F,
       wavelength: 2,
       brightness: SCAN_BRIGHTNESS,
-      hold_time: 10
+      hold_time: 10,
+      control: 0x01
     }).then(function () {
       console.log('[SCAN] 扫描指令发送成功，等待ADC回传...')
     }).catch(function (err) {