fix: add hex color validation to Category model and form (to solve #1247) (#1341)

- Added server-side validation to Category model to enforce 6-digit hex format for colors.
- Added HTML pattern attribute to category form for client-side validation.
- Updated tests to cover validation and fixed existing tests using shorthand hex colors.

test/models/budget_test.rb

@@ -264,7 +264,7 @@ class BudgetTest < ActiveSupport::TestCase
     source_budget.update!(budgeted_spending: 4000, expected_income: 6000)
 
     # Create a category only in the source budget
-    temp_category = Category.create!(name: "Temp #{Time.now.to_f}", family: family, color: "#aaa")
+    temp_category = Category.create!(name: "Temp #{Time.now.to_f}", family: family, color: "#aaaaaa")
     source_budget.budget_categories.create!(category: temp_category, budgeted_spending: 100, currency: "USD")
 
     target_budget = Budget.find_or_bootstrap(family, start_date: 1.month.ago)
@@ -283,7 +283,7 @@ class BudgetTest < ActiveSupport::TestCase
     target_budget = Budget.find_or_bootstrap(family, start_date: 1.month.ago)
 
     # Add a new category only to the target
-    new_category = Category.create!(name: "New #{Time.now.to_f}", family: family, color: "#bbb")
+    new_category = Category.create!(name: "New #{Time.now.to_f}", family: family, color: "#bbbbbb")
     target_budget.budget_categories.create!(category: new_category, budgeted_spending: 0, currency: "USD")
 
     target_budget.copy_from!(source_budget)

test/models/category_test.rb

@@ -40,4 +40,19 @@ class CategoryTest < ActiveSupport::TestCase
     assert names.all? { |name| name.is_a?(String) }
     assert_equal names, names.uniq  # No duplicates
   end
+
+  test "should accept valid 6-digit hex colors" do
+    [ "#FFFFFF", "#000000", "#123456", "#ABCDEF", "#abcdef" ].each do |color|
+      category = Category.new(name: "Category #{color}", color: color, lucide_icon: "shapes", family: @family)
+      assert category.valid?, "#{color} should be valid"
+    end
+  end
+
+  test "should reject invalid colors" do
+    [ "invalid", "#123", "#1234567", "#GGGGGG", "red", "ffffff", "#ffff", "" ].each do |color|
+      category = Category.new(name: "Category #{color}", color: color, lucide_icon: "shapes", family: @family)
+      assert_not category.valid?, "#{color} should be invalid"
+      assert_includes category.errors[:color], "is invalid"
+    end
+  end
 end