Fix systemd-networkd config file paths in STACK.md

Co-authored-by: danielbodnar <1790726+danielbodnar@users.noreply.github.com>

Author: Copilot

STACK.md

@@ -287,7 +287,7 @@ HelloTimeSec=2
 MaxAgeSec=20
 ```
 
-#### 📄 /usr/lib/systemd/system/10-tenant-bridge.network:
+#### 📄 /usr/lib/systemd/network/10-tenant-bridge.network:
 ```ini
 [Match]
 Name=br-tenant-%i
@@ -326,7 +326,7 @@ Endpoint=${PEER_ENDPOINT}:51820
 PersistentKeepalive=25
 ```
 
-#### 📄 /usr/lib/systemd/system/20-wg-tenant.network:
+#### 📄 /usr/lib/systemd/network/20-wg-tenant.network:
 ```ini
 [Match]
 Name=wg-tenant-%i
@@ -354,7 +354,7 @@ DestinationPort=4789
 MacLearning=yes
 ```
 
-#### 📄 /usr/lib/systemd/system/30-vxlan-tenant.network:
+#### 📄 /usr/lib/systemd/network/30-vxlan-tenant.network:
 ```ini
 [Match]
 Name=vxlan-tenant-%i
@@ -379,7 +379,7 @@ Kind=vlan
 Id=%i
 ```
 
-#### 📄 /usr/lib/systemd/system/40-vlan-tenant.network:
+#### 📄 /usr/lib/systemd/network/40-vlan-tenant.network:
 ```ini
 [Match]
 Name=vlan-tenant-%i