Fix doublepuppet appservice null URL to stop Synapse transaction retries

Synapse continuously retries HTTP transactions to any appservice with a
non-null URL. Setting url: null (not url: "") tells Synapse this appservice
has no HTTP endpoint, stopping the retry loop.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

setup-bridges.sh

@@ -21,7 +21,7 @@ mkdir -p appservices
 echo "Creating doublepuppet appservice configuration..."
 cat > appservices/doublepuppet.yaml << EOF
 id: doublepuppet
-url: ""
+url: null
 as_token: "$DOUBLEPUPPET_AS_TOKEN"
 hs_token: "$DOUBLEPUPPET_HS_TOKEN"
 sender_localpart: doublepuppet

templates/doublepuppet.yaml

@@ -3,7 +3,7 @@
 # Generate tokens with: openssl rand -hex 32
 
 id: doublepuppet
-url: ""
+url: null
 as_token: "{{DOUBLEPUPPET_AS_TOKEN}}"
 hs_token: "{{DOUBLEPUPPET_HS_TOKEN}}"
 sender_localpart: doublepuppet