perf: reduce PBKDF2 iterations to 100k for faster registration (#6)

600k → 100k iterations. Registration drops from 167ms to 31ms (5.4x).
Still well above security minimum for a game backend.
Requires nova_auth >= novaframework/nova_auth#2.

Author: Taure

config/dev_sys.config.src

@@ -10,6 +10,9 @@
             }}
         ]}
     ]},
+    {nova_auth, [
+        {pbkdf2_iterations, 100000}
+    ]},
     {nova, [
         {use_stacktrace, true},
         {environment, dev},

config/prod_sys.config.src

@@ -10,6 +10,9 @@
             }}
         ]}
     ]},
+    {nova_auth, [
+        {pbkdf2_iterations, 100000}
+    ]},
     {nova, [
         {use_stacktrace, false},
         {environment, prod},