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 In doing so, some parts of the codebase have become outdated, unnecessary, or overly-complex as a natural result of this feature prioritization.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

test/models/account/balance_calculator_test.rb

@@ -113,9 +113,9 @@ class Account::BalanceCalculatorTest < ActiveSupport::TestCase
     create_trade(securities(:msft), account: @account, date: 1.day.ago.to_date, qty: 20, price: 100)
 
     holdings = [
-      Account::Holding.new(date: Date.current, security: securities(:msft), amount: 2000),
-      Account::Holding.new(date: 1.day.ago.to_date, security: securities(:msft), amount: 2000),
-      Account::Holding.new(date: 2.days.ago.to_date, security: securities(:msft), amount: 0)
+      Account::Holding.new(date: Date.current, security: securities(:msft), amount: 2000, currency: "USD"),
+      Account::Holding.new(date: 1.day.ago.to_date, security: securities(:msft), amount: 2000, currency: "USD"),
+      Account::Holding.new(date: 2.days.ago.to_date, security: securities(:msft), amount: 0, currency: "USD")
     ]
 
     expected = [ 0, 20000, 20000, 20000 ]