Plaid sync domain improvements (#2267)

Breaks our Plaid sync process out into more manageable classes. Notably, this moves the sync process to a distinct, 2-step flow:

1. Import stage - we first make API calls and import Plaid data to "mirror" tables
2. Processing stage - read the raw data, apply business rules, build internal domain models and sync balances

This provides several benefits:

- Plaid syncs can now be "replayed" without fetching API data again
- Mirror tables provide better audit and debugging capabilities
- Eliminates the "all or nothing" sync behavior that is currently in place, which is brittle

app/views/transactions/_header.html.erb

@@ -15,6 +15,12 @@
     <% if entry.transaction.transfer? %>
       <%= icon "arrow-left-right", class: "mt-1" %>
     <% end %>
+
+    <% if entry.linked? %>
+      <span title="Linked with Plaid">
+        <%= icon("refresh-ccw", size: "sm") %>
+      </span>
+    <% end %>
   </div>
 
   <span class="text-sm text-secondary">

app/views/transactions/show.html.erb

@@ -18,6 +18,7 @@
           <%= f.date_field :date,
                 label: t(".date_label"),
                 max: Date.current,
+                disabled: @entry.linked?,
                 "data-auto-submit-form-target": "auto" %>
 
           <% unless @entry.transaction.transfer? %>
@@ -25,13 +26,15 @@
               <%= f.select :nature,
                     [["Expense", "outflow"], ["Income", "inflow"]],
                     { container_class: "w-1/3", label: t(".nature"), selected: @entry.amount.negative? ? "inflow" : "outflow" },
-                    { data: { "auto-submit-form-target": "auto" } } %>
+                    { data: { "auto-submit-form-target": "auto" }, disabled: @entry.linked? } %>
 
               <%= f.money_field :amount, label: t(".amount"),
                     container_class: "w-2/3",
                     auto_submit: true,
                     min: 0,
-                    value: @entry.amount.abs %>
+                    value: @entry.amount.abs,
+                    disabled: @entry.linked?,
+                    disable_currency: @entry.linked? %>
             </div>
 
             <%= f.fields_for :entryable do |ef| %>
@@ -66,7 +69,7 @@
             <%= f.fields_for :entryable do |ef| %>
 
               <%= ef.collection_select :merchant_id,
-                      Current.family.merchants.alphabetically,
+                    [@entry.transaction.merchant, *Current.family.merchants.alphabetically].compact,
                     :id, :name,
                     { include_blank: t(".none"),
                       label: t(".merchant_label"),