feat: AI MIDI Prompt Template & Preset Engine

- promptTemplateManager.js: standalone service with keyword scoring, CRUD, fav toggle
- ai_presets.py: backend CRUD router (JSON file, auth isolation)
- AIPresetModal: PromptTemplateManager, star/fav column, backend API sync
- Piano Roll AI: preset matching support
- 7 tests: matching, CRUD, anonymous auth, user isolation

app/static/js/services/api.js

@@ -66,6 +66,10 @@ window.API_BASE_URL = window.API_BASE_URL || window.location.origin;
         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/${sfId}`, { method: 'GET' }),
+        getAIPresets: () => apiRequest('/api/v1/ai/presets', { method: 'GET' }),
+        saveAIPreset: (preset) => apiRequest('/api/v1/ai/presets', { method: 'POST', body: JSON.stringify(preset) }),
+        deleteAIPreset: (presetId) => apiRequest(`/api/v1/ai/presets/${presetId}`, { method: 'DELETE' }),
+
         renderProject: (projectJson, outputFilename) => apiRequest('/api/v1/plugins/render', { method: 'POST', body: JSON.stringify({ project_json: projectJson, output_filename: outputFilename }) }),
         deleteSoundFont: (sfId) => apiRequest(`/api/v1/plugins/soundfont/${sfId}`, { method: 'DELETE' }),
         uploadSoundFont: async (file) => {