Implement SimpleFin API client and data models

- Add SimplefinItem model with sync capabilities and encryption
- Add SimplefinAccount model for account data mapping
- Implement Provider::Simplefin API client with token exchange
- Add SimpleFin protocol support with proper error handling
- Include sync jobs, importers, and processors for data flow
- Add family SimpleFin connectivity mixin

app/models/simplefin_account/processor.rb

@@ -0,0 +1,84 @@
+class SimplefinAccount::Processor
+  attr_reader :simplefin_account
+
+  def initialize(simplefin_account)
+    @simplefin_account = simplefin_account
+  end
+
+  def process
+    ensure_account_exists
+    process_transactions
+  end
+
+  private
+
+    def ensure_account_exists
+      return if simplefin_account.account.present?
+
+      account = Account.create_from_simplefin_account(simplefin_account)
+      simplefin_account.update!(account: account)
+    end
+
+    def process_transactions
+      return unless simplefin_account.raw_transactions_payload.present?
+
+      account = simplefin_account.account
+      transactions_data = simplefin_account.raw_transactions_payload
+
+      transactions_data.each do |transaction_data|
+        process_transaction(account, transaction_data)
+      end
+    end
+
+    def process_transaction(account, transaction_data)
+      # Convert SimpleFin transaction to internal Transaction format
+      amount_cents = parse_amount(transaction_data[:amount], account.currency)
+      posted_date = parse_date(transaction_data[:posted])
+
+      transaction_attributes = {
+        account: account,
+        name: transaction_data[:description] || "Unknown transaction",
+        amount: Money.new(amount_cents, account.currency),
+        date: posted_date,
+        currency: account.currency,
+        raw_data: transaction_data
+      }
+
+      # Use external ID to prevent duplicates
+      external_id = "simplefin_#{transaction_data[:id]}"
+
+      Transaction.find_or_create_by(external_id: external_id) do |transaction|
+        transaction.assign_attributes(transaction_attributes)
+      end
+    rescue => e
+      Rails.logger.error("Failed to process SimpleFin transaction #{transaction_data[:id]}: #{e.message}")
+      # Don't fail the entire sync for one bad transaction
+    end
+
+    def parse_amount(amount_value, currency)
+      case amount_value
+      when String
+        (BigDecimal(amount_value) * 100).to_i
+      when Numeric
+        (amount_value * 100).to_i
+      else
+        0
+      end
+    rescue ArgumentError
+      0
+    end
+
+    def parse_date(date_value)
+      case date_value
+      when String
+        Date.parse(date_value)
+      when Integer
+        # Unix timestamp
+        Time.at(date_value).to_date
+      else
+        Date.current
+      end
+    rescue ArgumentError, TypeError
+      Date.current
+    end
+end