README: remove most multi-line <br/> node labels from diagram, test #3

Compared node labels between this diagram and the non-gapped
architecture-overview.md one - this had 5 two-line labels, that one
only 2. Reduced to 1 remaining (App Host) to test whether multi-line
label height is what's breaking the container size calculation.

README.md

@@ -81,12 +81,12 @@ flowchart LR
     Internet(["Internet"]) --> Edge["Edge Firewall"]
     Edge --> LAN["LAN"]
 
-    LAN --> DNS["Internal DNS<br/>two zones"]
-    LAN --> Vault["Vault<br/>PKI + secrets"]
+    LAN --> DNS["Internal DNS"]
+    LAN --> Vault["Vault"]
     DNS --> Vault
 
     Vault --> Apps["App Host<br/>41 stacks"]
-    Vault --> Automation["Automation VM<br/>Git + orchestration"]
+    Vault --> Automation["Automation VM"]
     LAN --> FileServer["File Server"]
     DNS --> FileServer
     LAN --> Automation
@@ -94,7 +94,7 @@ flowchart LR
     Apps --> InternalProxy["Internal Proxy Zone"]
     Apps --> SSO["SSO"]
 
-    Vault --> EdgeProxy["User-Facing Proxy<br/>mTLS"]
+    Vault --> EdgeProxy["User-Facing Proxy"]
     DNS --> EdgeProxy
     Apps -.proxied.-> EdgeProxy
     SSO -.auth.-> EdgeProxy