feat(core): register system_settings router in main.py

app/main.py

@@ -40,6 +40,7 @@ from app.routes import (
     currencies,
     taxes,
     sequences,
+    system_settings,
 )
 
 
@@ -192,6 +193,7 @@ def create_app() -> FastAPI:
     app.include_router(currencies.router)
     app.include_router(taxes.router)
     app.include_router(sequences.router)
+    app.include_router(system_settings.router)
 
     # ── Register plugin routes (before SPA catch-all) ────────────────
     registry = get_registry()