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/templates/index.html

@@ -20,6 +20,7 @@
     <script src="/static/js/services/dawCommandDispatcher.js?v=202607271016"></script>
     <script src="/static/js/services/pianoRollTabService.js?v=202607272044"></script>
     <script src="/static/js/services/ghostNoteExtractor.js?v=202607271727"></script>
+    <script src="/static/js/services/promptTemplateManager.js?v=202607281039"></script>
     <script src="/static/js/app.precompiled.js?v=202607271245" defer></script>
     <link rel="stylesheet" href="/static/css/styles.css?v=202607271016">
     <style>