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/static/js/services/soundfontPlayer.js

@@ -30,9 +30,45 @@
         return window.__sharedAudioCtx;
     };
 
+    // ── Per-channel MIDI state (16 GM channels) ──
+    const _channels = Array.from({ length: 16 }, () => ({ bank: 0, program: 0, isPercussion: false }));
+    let _nextMelodicChannel = 0;
+
     const SonicSF = {
         loadedFonts: {},
 
+        controllerChange: function (channel, controller, value) {
+            if (channel < 0 || channel > 15) return;
+            if (controller === 0) {
+                _channels[channel].bank = value;
+                _channels[channel].isPercussion = (value === 128);
+            }
+        },
+
+        programChange: function (channel, program) {
+            if (channel < 0 || channel > 15) return;
+            _channels[channel].program = program;
+        },
+
+        allocateChannel: function (bank) {
+            if (bank === 128) return 9;
+            const ch = _nextMelodicChannel % 9;
+            _nextMelodicChannel = (_nextMelodicChannel + 1) % 9;
+            return ch;
+        },
+
+        applyAITrackInstrument: function (bank, program) {
+            const channel = this.allocateChannel(bank);
+            this.controllerChange(channel, 0, bank);
+            this.programChange(channel, program);
+            return channel;
+        },
+
+        getChannelState: function (channel) {
+            if (channel < 0 || channel > 15) return null;
+            return { ..._channels[channel] };
+        },
+
         // Load SoundFont from URL → ArrayBuffer → store in memory
         loadSoundFont: async function (url) {
             if (this.loadedFonts[url]) return this.loadedFonts[url];
@@ -43,7 +79,7 @@
             return buffer;
         },
 
-        playNote: function (note, velocity, durationMs, startTime, program, destinationNode) {
+        playNote: function (note, velocity, durationMs, startTime, program, destinationNode, channel) {
             const ctx = getCtx();
             const freq = 440 * Math.pow(2, (note - 69) / 12);
             if (freq <= 0 || isNaN(freq)) return null;
@@ -59,7 +95,11 @@
             let releaseTime = 0.2;
             let volFactor = 0.25;
 
-            const prog = program !== undefined ? parseInt(program) : 0;
+            let prog = program !== undefined ? parseInt(program) : 0;
+            if (channel !== undefined && channel >= 0 && channel < 16) {
+                const chState = _channels[channel];
+                prog = chState.program || prog;
+            }
             if (prog >= 0 && prog <= 7) { // Pianos
                 oscType = 'sine';
                 decayTime = 0.3;