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 In doing so, some parts of the codebase have become outdated, unnecessary, or overly-complex as a natural result of this feature prioritization.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

@@ -3,7 +3,7 @@
 <% accounts.group_by(&:accountable_type).sort_by { |group, _| group }.each do |group, accounts| %>
   <div class="bg-gray-25 p-1 rounded-xl">
     <div class="flex items-center px-4 py-2 text-xs font-medium text-secondary">
-      <p><%= to_accountable_title(Accountable.from_type(group)) %></p>
+      <p><%= Accountable.from_type(group).display_name %></p>
       <span class="text-subdued mx-2">&middot;</span>
       <p><%= accounts.count %></p>
       <p class="ml-auto"><%= totals_by_currency(collection: accounts, money_method: :balance_money) %></p>

app/views/accounts/index/_manual_accounts.html.erb

@@ -1,6 +1,6 @@
 <%# locals: (accounts:) %>
 
-<details open class="group bg-white p-4 border border-alpha-black-25 shadow-xs rounded-xl">
+<details open class="group bg-white p-4 shadow-border-xs rounded-xl">
   <summary class="flex items-center gap-2 focus-visible:outline-hidden">
     <%= lucide_icon "chevron-right", class: "group-open:transform group-open:rotate-90 text-secondary w-5" %>