perf(transactions): add kind to Transaction model and remove expensive Transfer joins in aggregations (#2388)

* add kind to transaction model

* Basic transfer creator

* Fix method naming conflict

* Creator form pattern

* Remove stale methods

* Tweak migration

* Remove BaseQuery, write entire query in each class for clarity

* Query optimizations

* Remove unused exchange rate query lines

* Remove temporary cache-warming strategy

* Fix test

* Update transaction search

* Decouple transactions endpoint from IncomeStatement

* Clean up transactions controller

* Update cursor rules

* Cleanup comments, logic in search

* Fix totals logic on transactions view

* Fix pagination

* Optimize search totals query

* Default to last 30 days on transactions page if no filters

* Decouple transactions list from transfer details

* Revert transfer route

* Migration reset

* Bundle update

* Fix matching logic, tests

* Remove unused code

app/models/transfer/creator.rb

@@ -0,0 +1,85 @@
+class Transfer::Creator
+  def initialize(family:, source_account_id:, destination_account_id:, date:, amount:)
+    @family = family
+    @source_account = family.accounts.find(source_account_id) # early throw if not found
+    @destination_account = family.accounts.find(destination_account_id) # early throw if not found
+    @date = date
+    @amount = amount.to_d
+  end
+
+  def create
+    transfer = Transfer.new(
+      inflow_transaction: inflow_transaction,
+      outflow_transaction: outflow_transaction,
+      status: "confirmed"
+    )
+
+    if transfer.save
+      source_account.sync_later
+      destination_account.sync_later
+    end
+
+    transfer
+  end
+
+  private
+    attr_reader :family, :source_account, :destination_account, :date, :amount
+
+    def outflow_transaction
+      name = "#{name_prefix} to #{destination_account.name}"
+
+      Transaction.new(
+        kind: outflow_transaction_kind,
+        entry: source_account.entries.build(
+          amount: amount.abs,
+          currency: source_account.currency,
+          date: date,
+          name: name,
+        )
+      )
+    end
+
+    def inflow_transaction
+      name = "#{name_prefix} from #{source_account.name}"
+
+      Transaction.new(
+        kind: "funds_movement",
+        entry: destination_account.entries.build(
+          amount: inflow_converted_money.amount.abs * -1,
+          currency: destination_account.currency,
+          date: date,
+          name: name,
+        )
+      )
+    end
+
+    # If destination account has different currency, its transaction should show up as converted
+    # Future improvement: instead of a 1:1 conversion fallback, add a UI/UX flow for missing rates
+    def inflow_converted_money
+      Money.new(amount.abs, source_account.currency)
+           .exchange_to(
+             destination_account.currency,
+             date: date,
+             fallback_rate: 1.0
+           )
+    end
+
+    # The "expense" side of a transfer is treated different in analytics based on where it goes.
+    def outflow_transaction_kind
+      if destination_account.loan?
+        "loan_payment"
+      elsif destination_account.liability?
+        "cc_payment"
+      else
+        "funds_movement"
+      end
+    end
+
+    def name_prefix
+      if destination_account.liability?
+        "Payment"
+      else
+        "Transfer"
+      end
+    end
+end