V45: D17 seamless loop wrap + D18 stop solo note-off (Qin) + D18b/c guard + engine VST load fixes

- D17: wrap_info/wrap-skip, fx wrap xfade, playhead-derived scheduling
- D18: solo stop -> NOTE_OFF all sounding timeline pitches + CC123/CC120
- D18b: track audible gain guard, tracksRef fallback
- D18c: timelinePitchesRef per-track Set, kill at applyAllTrackMuteSolo
- bridge ring _MAX 16, index v=202608290928
- plugins.py/vst_engine.py/fx_realtime.py/JuceFxEngine.cpp: VSTi load + Qin fixes (uncommitted 12:18)

app/core/vst_engine.py

@@ -1,9 +1,9 @@
 # SonicForge Studio VST / VSTi Engine Service
+from __future__ import annotations
 import os
 import json
 import re
 import time as _time
-import numpy as np
 import functools
 import threading
 from ctypes import c_char_p
@@ -52,6 +52,7 @@ def render_soundfont_midi_to_audio(midi_events: list, sf_path: str, bank: int =
     Xử lí đúng note CHỒNG nhau + đuôi release (event-stream noteon/noteoff).
     Trả stereo float32 (2, N). Raise RuntimeError nếu pyfluidsynth thiếu / SF
     không load được."""
+    import numpy as np
     import fluidsynth as _fs
     settings = _fs.new_fluid_settings()
     _fs.fluid_settings_setnum(settings, b'synth.sample-rate', float(sr))
@@ -112,6 +113,7 @@ def render_soundfont_midi_to_audio(midi_events: list, sf_path: str, bank: int =
 
 @_render_locked
 def render_midi_events_to_audio(midi_events: list, sr: int = 44100, bpm: float = 120.0, instrument: str = 'synth') -> np.ndarray:
+    import numpy as np
     beat_duration_sec = 60.0 / max(30.0, bpm)
     max_duration_sec = 2.0
     for event in midi_events: