wrapper: leading low hum to prime Discord (configurable MS/HZ/DB)

docs/TTS-DESIGN.md

@@ -234,6 +234,15 @@ record what the engine needs to interpret, add, or hide._
   Measured on a Keith Bell line: first sample >30 at 22.6 ms, speech (>500) at 29.6 ms,
   attack rising naturally over about 15 ms, tail decaying over about 18 ms. No click and
   no attenuation of the first word; Veskslop's 150 ms playback lead-in sits on top.
+- Leading hum (on by default): 80 ms of a 75 Hz sine at -48 dBFS peak is prepended
+  before the engine padding, to keep Discord's audio pipeline open so the first word is
+  not gated. Configurable: `VESKSLOP_TTS_HUM_MS` (0 disables), `_HUM_HZ` (30-200),
+  `_HUM_DB` (-80..-6). It sits about 45 dB under the speech peak; raise `_HUM_DB` toward
+  -36 if a client still gates the start, lower it for stealth. Generated in the same
+  ffmpeg pass (no extra process) and not part of the EBU measurement, so the documented
+  loudness/peak targets still hold. Measured: hum 75.0 Hz / -48.0 dBFS, speech onset at
+  about 110 ms, final -18.6 LUFS / -3.0 dBFS; `HUM_MS=0` reproduces the previous output
+  byte-for-byte.
 
 ### Voice IDs