P0 HOTFIX: Subscription asset_limit calculation fix

Root cause: Old code used rules.get('max_vehicles') which only searched
JSONB root level. Corporate tiers store limits under rules['allowances'].

Changes:
1. Added _extract_limit() helper (3-level search: direct → allowances → limits)
2. Replaced single-sub .limit(1) with multi-sub .all() for true aggregation
3. Fixed fallback path to use _extract_limit() instead of rules.get()
4. Added clamping: asset_limit = max(asset_limit, 1) right before
   SubscriptionSummary creation on BOTH code paths
5. Added 'type' column to SubscriptionTier model (base vs addon)

backend/app/models/core_logic.py

@@ -69,6 +69,10 @@ class SubscriptionTier(Base):
     """
     Előfizetési csomagok definíciója (pl. Free, Premium, VIP).
     A csomagok határozzák meg a korlátokat (pl. max járműszám).
+    
+    P0 MULTI-SUBSCRIPTION AGGREGATION:
+    A `type` mező különbözteti meg a Base tier-eket ('private', 'corporate', 'business')
+    az Add-on tier-ektől ('addon'). Ez lehetővé teszi az "1 Base + N Add-on" modellt.
     """
     __tablename__ = "subscription_tiers"
     __table_args__ = {"schema": "system"}
@@ -78,6 +82,18 @@ class SubscriptionTier(Base):
     rules: Mapped[dict] = mapped_column(JSONB, server_default=text("'{}'::jsonb")) # pl. {"max_vehicles": 5}
     is_custom: Mapped[bool] = mapped_column(Boolean, default=False)
 
+    # ── P0 MULTI-SUBSCRIPTION AGGREGATION: Base vs Add-on típus ──
+    # 'base' = core tier (individual, corporate, business)
+    # 'addon' = add-on tier (extra vehicles, branches, users)
+    # None/empty = treated as 'base' for backward compatibility
+    type: Mapped[Optional[str]] = mapped_column(
+        String(20),
+        nullable=True,
+        default=None,
+        server_default=text("NULL"),
+        comment="Tier type: 'base' for core subscriptions, 'addon' for add-on tiers. NULL = base (backward compat)."
+    )
+
     # ── P0 3D CAPABILITY MATRIX: feature_capabilities JSONB ──
     # Defines what features/capabilities this subscription tier unlocks.
     # Example: {"can_export_data": True, "can_use_analytics": True, "max_vehicles": 50}