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 In doing so, some parts of the codebase have become outdated, unnecessary, or overly-complex as a natural result of this feature prioritization.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

@@ -0,0 +1,25 @@
+class AccountableSparklinesController < ApplicationController
+  def show
+    @accountable = Accountable.from_type(params[:accountable_type]&.classify)
+
+    @series = Rails.cache.fetch(cache_key) do
+      family.accounts.active
+              .where(accountable_type: @accountable.name)
+              .balance_series(
+                currency: family.currency,
+                favorable_direction: @accountable.favorable_direction
+              )
+    end
+
+    render layout: false
+  end
+
+  private
+    def family
+      Current.family
+    end
+
+    def cache_key
+      family.build_cache_key("#{@accountable.name}_sparkline")
+    end
+end