New Design System + Codebase Refresh (#1823)

Since the very first 0.1.0-alpha.1 release, we've been moving quickly to add new features to the Maybe app. In doing so, some parts of the codebase have become outdated, unnecessary, or overly-complex as a natural result of this feature prioritization.

Now that "core" Maybe is complete, we're moving into a second phase of development where we'll be working hard to improve the accuracy of existing features and build additional features on top of "core". This PR is a quick overhaul of the existing codebase aimed to:

- Establish the brand new and simplified dashboard view (pictured above)
- Establish and move towards the conventions introduced in Cursor rules and project design overview #1788
- Consolidate layouts and improve the performance of layout queries
- Organize the core models of the Maybe domain (i.e. Account::Entry, Account::Transaction, etc.) and break out specific traits of each model into dedicated concerns for better readability
- Remove stale / dead code from codebase
- Remove overly complex code paths in favor of simpler ones

app/models/budget_category.rb

@@ -6,7 +6,7 @@ class BudgetCategory < ApplicationRecord
 
   validates :budget_id, uniqueness: { scope: :category_id }
 
-  monetize :budgeted_spending, :actual_spending, :available_to_spend
+  monetize :budgeted_spending, :available_to_spend, :avg_monthly_expense, :median_monthly_expense, :actual_spending
 
   class Group
     attr_reader :budget_category, :budget_subcategories
@@ -45,12 +45,24 @@ class BudgetCategory < ApplicationRecord
     super || budget.family.categories.uncategorized
   end
 
-  def subcategory?
-    category.parent_id.present?
+  def name
+    category.name
   end
 
   def actual_spending
-    category.month_total(date: budget.start_date)
+    budget.budget_category_actual_spending(self)
+  end
+
+  def avg_monthly_expense
+    budget.category_avg_monthly_expense(category)
+  end
+
+  def median_monthly_expense
+    budget.category_median_monthly_expense(category)
+  end
+
+  def subcategory?
+    category.parent_id.present?
   end
 
   def available_to_spend