Fix Unicode env parsing in infra_secrets for stage startup.

Use unicode:characters_to_binary for os:getenv values so Cyrillic placeholder passwords fail with weak_secret instead of badarg crash.

Co-authored-by: Cursor <cursoragent@cursor.com>

test/unit/infra_secrets_tests.erl

@@ -26,7 +26,8 @@ infra_secrets_test_() ->
     {"stage rejects missing JWT_SECRET", fun test_stage_missing_jwt/0},
     {"stage rejects weak JWT_SECRET", fun test_stage_weak_jwt/0},
     {"stage accepts strong secrets", fun test_stage_strong_ok/0},
-    {"require_admin_seed_password rejects 123456", fun test_weak_admin_password/0}
+    {"require_admin_seed_password rejects 123456", fun test_weak_admin_password/0},
+    {"require_admin_seed_password rejects cyrillic placeholder", fun test_cyrillic_placeholder_password/0}
   ]}.
 
 test_dev_missing_ok() ->
@@ -60,3 +61,8 @@ test_weak_admin_password() ->
   os:putenv("ADMIN_PASSWORD", "123456"),
   ?assertMatch({error, {weak_secret, 'ADMIN_PASSWORD'}},
     infra_secrets:require_admin_seed_password("ADMIN_PASSWORD")).
+
+test_cyrillic_placeholder_password() ->
+  os:putenv("ADMIN_PASSWORD", "замените"),
+  ?assertMatch({error, {weak_secret, 'ADMIN_PASSWORD'}},
+    infra_secrets:require_admin_seed_password("ADMIN_PASSWORD")).