Feature: Referral-Rabattstufen — 10→20%, 20→30%, 50→50% lebenslang

- auth.py: _referral_tier() + _referral_next() Tier-Logik, GET /api/auth/referral gibt discount_pct + next_tier zurück
- settings.js: Referral-UI komplett neu — Tier-Kacheln, Fortschrittsbalken, Zähler, Rabatt-Hinweis
- SW by-v517, APP_VER 494

backend/routes/auth.py

@@ -149,6 +149,24 @@ async def logout(response: Response):
     return {"ok": True}
 
 
+_REFERRAL_TIERS = [
+    (50, 50),
+    (20, 30),
+    (10, 20),
+]
+
+def _referral_tier(count: int):
+    for threshold, discount in _REFERRAL_TIERS:
+        if count >= threshold:
+            return discount
+    return 0
+
+def _referral_next(count: int):
+    for threshold, discount in reversed(_REFERRAL_TIERS):
+        if count < threshold:
+            return {"count": threshold, "discount": discount}
+    return None  # Maximalstufe erreicht
+
 @router.get("/referral")
 async def get_referral_info(user=Depends(get_current_user)):
     with db() as conn:
@@ -162,11 +180,14 @@ async def get_referral_info(user=Depends(get_current_user)):
         if not code:
             code = _gen_referral_code()
             conn.execute("UPDATE users SET referral_code=? WHERE id=?", (code, user['id']))
-    base = os.getenv("APP_URL", "https://banyaro.app")
+    count = row["count"] if row else 0
+    base  = os.getenv("APP_URL", "https://banyaro.app")
     return {
-        "code":  code,
-        "count": row["count"] if row else 0,
-        "link":  f"{base}/?ref={code}",
+        "code":          code,
+        "count":         count,
+        "link":          f"{base}/?ref={code}",
+        "discount_pct":  _referral_tier(count),
+        "next_tier":     _referral_next(count),
     }