host: volume option; docs: voice adjustments beyond speed (volume, Flextalk profile)

docs/NOTES.md

@@ -82,6 +82,12 @@ final file `WatsonUNInstall.dll` is incomplete).
   Verified with the corrected DWORD registry: Kerry 0 st = 209 Hz, -6 st = 148 Hz,
   +6 st = 250 Hz (clamped at max); Keith 0 st = 119 Hz, +6 st = 170 Hz.
 - The wrapper maps semitones as `natural * 2^(st/12)` and clamps to the range.
+- volume: available through `ITTSAttributes` (host flag `-V`). Flextalk is linear
+  (0-65535, default 65535; half is about -6 dB). MSTTS is non-linear (0 = silence,
+  4096 about -24 dB, 65535+ full scale); treat it as on/off.
+- Flextalk per-speaker profile values are applied at voice load; `Expression` was
+  verified audible (0/59/100 produce different waveforms at equal duration). Changing
+  them requires a registry edit and re-selecting the voice.
 
 ## Decompiled corpora (Ghidra)