feat: Credits-System — Token-Usage-Router, Budget-Verwaltung, Frontend-Übersicht

- Neuer Router /api/token-usage mit Overview, Org-Detail, Monatsstatistik
- Budget-Felder (credits_total, cost_per_credit, token_budget_usd) bei Lizenz-Erstellung
- Token-Nutzung Sub-Tab in Org-Detail mit Verbrauchsbalken und Monatstabelle
- Dashboard Stat-Card für API-Kosten gesamt
- CSS Dark-Theme Styling für Token-Komponenten

src/main.py

@@ -10,7 +10,7 @@ from config import STATIC_DIR, PORT
 from database import db_dependency
 from auth import verify_password, create_token
 from models import LoginRequest, TokenResponse
-from routers import organizations, licenses, users, dashboard, sources
+from routers import organizations, licenses, users, dashboard, sources, token_usage
 
 import aiosqlite
 
@@ -40,6 +40,7 @@ app.include_router(licenses.router)
 app.include_router(users.router)
 app.include_router(dashboard.router)
 app.include_router(sources.router)
+app.include_router(token_usage.router)
 
 
 # --- Login ---