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 In doing so, some parts of the codebase have become outdated, unnecessary, or overly-complex as a natural result of this feature prioritization.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

@@ -1,5 +1,5 @@
 <%= turbo_frame_tag dom_id(@account, "valuations") do %>
-  <div class="bg-white space-y-4 p-5 border border-alpha-black-25 rounded-xl shadow-xs">
+  <div class="bg-white space-y-4 p-5 shadow-border-xs rounded-xl">
     <div class="flex items-center justify-between">
       <%= tag.h2 t(".valuations"), class: "font-medium text-lg" %>
       <%= link_to new_account_valuation_path(@account),
@@ -18,7 +18,7 @@
         <%= tag.div class: "col-span-1" %>
       </div>
 
-      <div class="rounded-lg bg-white border-alpha-black-25 shadow-xs">
+      <div class="rounded-lg bg-white shadow-border-xs">
         <%= turbo_frame_tag dom_id(@account.entries.account_valuations.new) %>
 
         <% if @entries.any? %>