Add credo

mix.exs

@@ -64,6 +64,7 @@ defmodule BirdyChat.MixProject do
       {:jason, "~> 1.2"},
       {:dns_cluster, "~> 0.2.0"},
       {:bandit, "~> 1.5"},
+      {:credo, "~> 1.0", only: [:dev, :test]},
 
       # Phoenix sockets client
       {:slipstream, "~> 1.0"},
@@ -90,7 +91,13 @@ defmodule BirdyChat.MixProject do
         "esbuild birdy_chat --minify",
         "phx.digest"
       ],
-      precommit: ["compile --warnings-as-errors", "deps.unlock --unused", "format", "test"]
+      precommit: [
+        "compile --warnings-as-errors",
+        "credo --strict",
+        "deps.unlock --unused",
+        "format",
+        "test"
+      ]
     ]
   end
 end