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 In doing so, some parts of the codebase have become outdated, unnecessary, or overly-complex as a natural result of this feature prioritization.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

@@ -0,0 +1,11 @@
+<%= turbo_frame_tag "#{@accountable.model_name.param_key}_sparkline" do %>
+  <div class="flex items-center justify-end gap-1">
+    <div class="w-8 h-3">
+      <%= render "shared/sparkline", id: dom_id(@accountable, :sparkline_chart), series: @series %>
+    </div>
+
+    <%= tag.p @series.trend.percent_formatted,
+              style: "color: #{@series.trend.color}",
+              class: "text-right text-xs font-medium text-primary" %>
+  </div>
+<% end %>