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/main.py

@@ -12,6 +12,7 @@ from app.api.v1.admin import router as admin_router
 from app.api.v1.projects import router as projects_router
 from app.api.v1.user_config import router as user_config_router
 from app.api.v1.ai_proxy import router as ai_proxy_router
+from app.api.v1.ai_presets import router as ai_presets_router
 from app.api.v1.plugins import router as plugins_router
 from app.core.auth import seed_admin
 from app.core.soundfont_converter import SoundFontConverter
@@ -50,6 +51,7 @@ app.include_router(admin_router, prefix="/api/v1/admin", tags=["admin"])
 app.include_router(projects_router, prefix="/api/v1/projects", tags=["projects"])
 app.include_router(user_config_router, prefix="/api/v1/user", tags=["user_config"])
 app.include_router(ai_proxy_router, prefix="/api/v1/ai", tags=["ai"])
+app.include_router(ai_presets_router, prefix="/api/v1/ai", tags=["ai"])
 app.include_router(plugins_router, prefix="/api/v1/plugins", tags=["plugins"])
 
 # Seed admin user on startup