Validate User name presence and handle blank names gracefully

Addresses an issue where User#familiar_name assumed `name` was always
present, potentially raising an exception during view rendering. Now
User validates name presence, and User#familiar_name handles blank
strings without error, in case any existing invalid records exist.

test/controllers/signup/completions_controller_test.rb

@@ -29,7 +29,7 @@ class Signup::CompletionsControllerTest < ActionDispatch::IntegrationTest
     assert_response :redirect, "Valid params should redirect"
   end
 
-  test "create with invalid params" do
+  test "create with blank name" do
     untenanted do
       post signup_completion_path, params: {
         signup: {
@@ -38,6 +38,9 @@ class Signup::CompletionsControllerTest < ActionDispatch::IntegrationTest
       }
     end
 
-    assert_response :unprocessable_entity, "Invalid params should return unprocessable entity"
+    assert_response :unprocessable_entity
+    assert_select ".txt-negative" do
+      assert_select "li", text: "Full name can't be blank"
+    end
   end
 end

test/models/user_test.rb

@@ -39,6 +39,27 @@ class UserTest < ActiveSupport::TestCase
     assert_equal "ÉLH", User.new(name: "Éva-Louise Hernández").initials
   end
 
+  test "name methods handle blank names gracefully" do
+    user = User.new(name: "")
+    assert_equal "", user.familiar_name
+    assert_nil user.first_name
+    assert_nil user.last_name
+    assert_equal "", user.initials
+  end
+
+  test "validates name presence" do
+    user = User.new(account: accounts("37s"), role: "member", name: "")
+    assert_not user.valid?
+    assert_includes user.errors[:name], "can't be blank"
+
+    user.name = "   "
+    assert_not user.valid?
+    assert_includes user.errors[:name], "can't be blank"
+
+    user.name = "Victor Cooper"
+    assert user.valid?
+  end
+
   test "setup?" do
     user = users(:kevin)