chore: add run-backend recipe (#306)

Also configure the domain to localhost in the local setup.

Author: boxdot

justfile

@@ -93,4 +93,8 @@ analyze-dart:
 # run Flutter tests
 [working-directory: 'app']
 test-flutter *args='':
-    flutter test {{args}}
+    flutter test
+
+# run backend server (at localhost)
+run-backend: init-db
+    cargo run --bin phnxserver

server/configuration/local.yaml

@@ -3,4 +3,5 @@
 # SPDX-License-Identifier: AGPL-3.0-or-later
 
 application:
+  domain: localhost
   host: 127.0.0.1