Add investment activity detection, labels, and exclusions

- Introduced `InvestmentActivityDetector` to mark internal investment activity as excluded from cashflow and assign appropriate labels.
- Added `exclude_from_cashflow` flag to `entries` and `investment_activity_label` to `transactions` with migrations.
- Implemented rake tasks to backfill and clear investment activity labels.
- Updated `PlaidAccount::Investments::TransactionsProcessor` to map Plaid transaction types to labels.
- Included comprehensive test coverage for new functionality.

test/models/transaction_test.rb

@@ -18,4 +18,37 @@ class TransactionTest < ActiveSupport::TestCase
 
     assert_not transaction.pending?
   end
+
+  test "investment_contribution is a valid kind" do
+    transaction = Transaction.new(kind: "investment_contribution")
+
+    assert_equal "investment_contribution", transaction.kind
+    assert transaction.investment_contribution?
+  end
+
+  test "all transaction kinds are valid" do
+    valid_kinds = %w[standard funds_movement cc_payment loan_payment one_time investment_contribution]
+
+    valid_kinds.each do |kind|
+      transaction = Transaction.new(kind: kind)
+      assert_equal kind, transaction.kind, "#{kind} should be a valid transaction kind"
+    end
+  end
+
+  test "INTERNAL_ACTIVITY_LABELS contains expected labels" do
+    assert_includes Transaction::INTERNAL_ACTIVITY_LABELS, "Buy"
+    assert_includes Transaction::INTERNAL_ACTIVITY_LABELS, "Sell"
+    assert_includes Transaction::INTERNAL_ACTIVITY_LABELS, "Reinvestment"
+    assert_includes Transaction::INTERNAL_ACTIVITY_LABELS, "Exchange"
+  end
+
+  test "ACTIVITY_LABELS contains all valid labels" do
+    assert_includes Transaction::ACTIVITY_LABELS, "Buy"
+    assert_includes Transaction::ACTIVITY_LABELS, "Sell"
+    assert_includes Transaction::ACTIVITY_LABELS, "Sweep In"
+    assert_includes Transaction::ACTIVITY_LABELS, "Sweep Out"
+    assert_includes Transaction::ACTIVITY_LABELS, "Dividend"
+    assert_includes Transaction::ACTIVITY_LABELS, "Interest"
+    assert_includes Transaction::ACTIVITY_LABELS, "Fee"
+  end
 end