V45.38: suppress iZotope 0x7E dialog

- _is_vst2_dll: pure-Python PE export-table check (magic-aware dd offset
  PE32+112) -> IZOzone11Core.dll (runtime lib, no VSTPluginMain) dropped
  from VST2 lists in _scan_plugins and list_scan_all; plugins.py same.
- _hidden_desktop_startupinfo: scan subprocess runs on hidden desktop
  (user32 CreateDesktopW, HDESK restype) -> third-party MessageBox invisible.
- SetErrorMode(SEM_FAILCRITICALERRORS|SEM_NOOPENFILEERRORBOX) in all 4
  bridge mains: missing dependency DLL fails silently instead of blocking.

app/api/v1/plugins.py

@@ -4,7 +4,7 @@ from fastapi.responses import FileResponse
 from pydantic import BaseModel
 from typing import Optional, Any
 from app.config import settings
-from app.core.vst_engine import PluginManager, HAS_PYFLUIDSYNTH, render_soundfont_midi_to_audio, RENDER_LOCK, _render_locked
+from app.core.vst_engine import PluginManager, HAS_PYFLUIDSYNTH, render_soundfont_midi_to_audio, RENDER_LOCK, _render_locked, _is_vst2_dll
 from app.core.soundfont_inspector import SoundFontInspector
 from app.core.soundfont_converter import SoundFontConverter
 from app.core.soundfont_scanner import SoundFontAutoScanner
@@ -348,7 +348,8 @@ def _scan_vst_in_dirs(dirs: list) -> list:
                             "id": name, "name": name, "type": "VST3",
                             "path": os.path.join(root, f),
                         }
-                elif low.endswith(".dll") and not has_vst3_file:
+                elif (low.endswith(".dll") and not has_vst3_file
+                      and _is_vst2_dll(os.path.join(root, f))):
                     name = os.path.splitext(f)[0]
                     if name not in found:
                         found[name] = {