Adds a real Pitch Bend VST3 parameter (plus-minus 12 semitones, automatable)
separate from Vowel. The hardware MIDI pitch wheel is routable to
either Vowel (Classic / Delay Lama compat, default) or Pitch via a
new right-click submenu; the host is notified via
restartComponent(kMidiCCAssignmentChanged) so the switch takes effect
without a plugin reload. The submenu label reflects the active mode.

DSP changes apply the pitch offset in MIDI-note space inside the voice
synthesis loop, upstream of the Hz-space unison detune, so all unison
voices shift together while preserving their spread. Dead
monk_synth_pitch_bend function (which just redirected to set_vowel)
removed.

Refactors the DSP sources into a monk_dsp static library so the plugin
and a new opt-in test target can both link the same objects. Adds a
minimal assert.h + CTest suite covering pitch-bend clamping, ADSR
envelope boundaries, note-stack LIFO, unison detune math, and delay
feedback stability. Tests are gated behind -DMONKSYNTH_BUILD_TESTS=ON
and run on the Linux CI job before packaging so regressions block
releases.

Pitch Bend submenu localized into English, Japanese, and Korean.