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 In doing so, some parts of the codebase have become outdated, unnecessary, or overly-complex as a natural result of this feature prioritization.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

@@ -1,6 +1,6 @@
-<div data-controller="modal" data-modal-open-value="true" class="absolute inset-0 z-50 flex items-center justify-center bg-white/90" aria-labelledby="modal-title" role="dialog" aria-modal="true">
+<div data-controller="modal" data-modal-open-value="true" class="h-full flex items-center justify-center bg-white/90" aria-labelledby="modal-title" role="dialog" aria-modal="true">
   <div class="w-[400px] rounded-xl relative overflow-hidden">
-    <div class="bg-white shadow-xl border border-gray-200 rounded-xl relative z-10">
+    <div class="bg-white shadow-border-xs rounded-xl relative z-10">
       <div class="rounded-xl" style="background-image: url('<%= asset_path("maybe-plus-background.svg") %>'); background-size: cover; background-position: center top;">
         <div class="text-center rounded-xl" style="background-image: linear-gradient(to bottom, rgba(197,161,119,0.15) 0%, rgba(255,255,255,0.8) 30%, white 40%);">
           <div class="p-4 pt-2 rounded-xl">