nix: Fix PostgreSQL init role issues in process-compose setup

Create a dummy 'postgres' role to silence the "role postgres does not
exist" log spam, and set PGUSER environment variable on init processes
so psql connects as the OS user (matching what initdb created).

Author: lutter

flake.nix

@@ -90,6 +90,7 @@
             inherit port dataDir;
             initialScript = {
               before = ''
+                CREATE ROLE postgres WITH LOGIN;
                 CREATE USER \"${user}\" WITH PASSWORD '${password}' SUPERUSER;
               '';
             };
@@ -140,6 +141,11 @@
               database = "graph-test";
             };
 
+            # Set PGUSER so psql connects as the OS user (matching initdb's superuser)
+            settings.processes."postgres-unit-init".environment = {
+              PGUSER = builtins.getEnv "USER";
+            };
+
             services.ipfs."ipfs-unit" = {
               enable = true;
               dataDir = "./.data/unit/ipfs";
@@ -172,6 +178,11 @@
               database = "graph-node";
             };
 
+            # Set PGUSER so psql connects as the OS user (matching initdb's superuser)
+            settings.processes."postgres-integration-init".environment = {
+              PGUSER = builtins.getEnv "USER";
+            };
+
             services.ipfs."ipfs-integration" = {
               enable = true;
               dataDir = "./.data/integration/ipfs";