perf(dashboard): streamline investment activity totals (#2257)

* perf(dashboard): streamline investment activity totals

* fix(dashboard): skip empty investment totals cache writes

Short-circuit empty investment account totals before cache fetch and move the new SQL query capture regression helper into test/support.

* refactor(dashboard): address review on investment totals query

- Drop defensive ArgumentError guards in InvestmentStatement::Totals#initialize.
  The sole caller (totals_query) always passes correct types, and the
  empty_result early-return already handles the zero-accounts case.
- Remove the redundant accounts JOIN and its family_id/status filters from the
  aggregation SQL. account_ids is already scoped to the family's visible
  (draft/active) investment accounts, so the join back to accounts is
  unnecessary work in the query plan. Drop the now-unused family_id param.
- Add a regression assertion that the aggregate no longer joins accounts.

test/support/sql_query_capture.rb

@@ -0,0 +1,17 @@
+module SqlQueryCapture
+  def capture_sql_queries
+    queries = []
+    callback = lambda do |_name, _started, _finished, _unique_id, payload|
+      next if payload[:cached]
+      next if %w[SCHEMA TRANSACTION].include?(payload[:name])
+
+      queries << payload[:sql].squish
+    end
+
+    ActiveSupport::Notifications.subscribed(callback, "sql.active_record") do
+      yield
+    end
+
+    queries
+  end
+end