feat: add SoundFont inspection engine + AI instrument schema

- SoundFontInspector (sf2utils) scans .sf2, generates full/condensed catalog
- GET /api/v1/plugins/soundfonts/catalog with lazy init + cache invalidation
- AI tool generate_multitrack_midi now requires soundfont_id/bank/program
- Condensed catalog auto-injected into AI system prompt with bank rules
- Server render: FluidSynth program_select uses bank/program + channel routing (drums→ch9)
- VST3 pedalboard path inserts CC0 bank select + program change before notes
- DecentSamplerManager loads .dspreset with CWD fix for relative sample paths
- Pianobook render branch in render_engine.py
- Client SonicSF: controllerChange, programChange, applyAITrackInstrument
- Post-AI track creation applies instrument via applyAITrackInstrument
- Background cache rescan on .sf2 upload, frontend re-fetches catalog
- libcurl4 + VST3 dirs in Dockerfile

app/core/vst_engine.py

@@ -286,11 +286,15 @@ class PluginManager:
         }
 
     @staticmethod
-    def midi_events_to_messages(midi_events: list, bpm: float, sr: int) -> list:
+    def midi_events_to_messages(midi_events: list, bpm: float, sr: int, bank: int = None, program: int = None) -> list:
         if not HAS_PEDALBOARD:
             return []
         beat_duration_sec = 60.0 / max(30.0, bpm)
         messages = []
+        if bank is not None:
+            messages.append(MidiMessage(control_change=0, value=bank, sample_offset=0))
+        if program is not None:
+            messages.append(MidiMessage(program_change=program, sample_offset=0))
         for ev in midi_events:
             note = ev.get("note", 60)
             velocity = ev.get("velocity", 100)
@@ -313,3 +317,29 @@ class PluginManager:
         if data[8:12] != b'sfbk':
             return False
         return True
+
+
+class DecentSamplerManager:
+    def __init__(self, vst_path="/opt/daw_engine/vst3/DecentSampler.vst3"):
+        self.vst_path = vst_path
+
+    def create_decent_sampler_instance(self, dspreset_path: str):
+        if not HAS_PEDALBOARD:
+            raise RuntimeError("pedalboard not available")
+        if not os.path.exists(self.vst_path):
+            raise FileNotFoundError(f"DecentSampler VST3 not found at {self.vst_path}")
+        if not os.path.exists(dspreset_path):
+            raise FileNotFoundError(f"Preset file not found at {dspreset_path}")
+
+        plugin = VST3Plugin(self.vst_path)
+
+        abs_preset = os.path.abspath(dspreset_path)
+        preset_dir = os.path.dirname(abs_preset)
+        cwd_before = os.getcwd()
+        try:
+            os.chdir(preset_dir)
+            plugin.load_preset(abs_preset)
+        finally:
+            os.chdir(cwd_before)
+
+        return plugin