feat: Credits-System mit Verbrauchsanzeige im User-Dropdown

- DB-Migration: credits_total/credits_used/cost_per_credit auf licenses, token_usage_monthly Tabelle
- Orchestrator: Monatliche Token-Aggregation + Credits-Abzug nach Refresh
- Auth: Credits-Daten im /me Endpoint + Bugfix fehlende Klammer in get()
- Frontend: Credits-Balken im User-Dropdown mit Farbwechsel

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/routers/auth.py

@@ -261,10 +261,28 @@ async def get_me(
         from services.license_service import check_license
         license_info = await check_license(db, current_user["tenant_id"])
 
+    # Credits-Daten laden
+    credits_total = None
+    credits_remaining = None
+    credits_percent_used = None
+    if current_user.get("tenant_id"):
+        lic_cursor = await db.execute(
+            "SELECT credits_total, credits_used, cost_per_credit FROM licenses WHERE organization_id = ? AND status = 'active' ORDER BY id DESC LIMIT 1",
+            (current_user["tenant_id"],))
+        lic_row = await lic_cursor.fetchone()
+        if lic_row and lic_row["credits_total"]:
+            credits_total = lic_row["credits_total"]
+            credits_used = lic_row["credits_used"] or 0
+            credits_remaining = max(0, int(credits_total - credits_used))
+            credits_percent_used = round(min(100, (credits_used / credits_total) * 100), 1) if credits_total > 0 else 0
+
     return UserMeResponse(
         id=current_user["id"],
         username=current_user["username"],
         email=current_user.get("email", ""),
+        credits_total=credits_total,
+        credits_remaining=credits_remaining,
+        credits_percent_used=credits_percent_used,
         role=current_user["role"],
         org_name=org_name,
         org_slug=current_user.get("org_slug", ""),