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/api.js

@@ -63,6 +63,7 @@ window.API_BASE_URL = window.API_BASE_URL || window.location.origin;
         savePreferences: (prefs) => apiRequest('/api/v1/user/preferences', { method: 'POST', body: JSON.stringify({ preferences: prefs }) }),
 
         listPlugins: () => apiRequest('/api/v1/plugins/available', { method: 'GET' }),
+        getSoundfontCatalog: () => apiRequest('/api/v1/plugins/soundfonts/catalog', { method: 'GET' }),
         listDefaultSoundfonts: () => apiRequest('/api/v1/plugins/default-soundfonts', { method: 'GET' }),
         listSoundfontInstruments: (sfId) => apiRequest(`/api/v1/plugins/soundfont-instruments/${sfId}`, { method: 'GET' }),
         renderProject: (projectJson, outputFilename) => apiRequest('/api/v1/plugins/render', { method: 'POST', body: JSON.stringify({ project_json: projectJson, output_filename: outputFilename }) }),