Perf/dashboard endpoint optimization (#1897)

* optimize net_category_totals() by using memoized cache

* fix issue - net_category_totals cache is never populated - suggested by coderabbitAI

* fix 422 error for service-worker

* remove warning of [assigned but unused variables] - income_statement.rb

* remove warnings of [assigned but unused] from Prism - income_statement_test.rb

* add some measurements to improve docstring coverage, follow CodeRabbit recommendation

* attach Skylight monitoring for dev env as well - use my own Skylight auth token

* integrate Skylight with my own account auth token for local benchmark

* fix PR review suggestion - Move fallback release-note copy to i18n keys

* follow PR review - Fix changelog GitHub fetch timeout bounding

* FIX - Variable shadowing; Prefer stubbing the specific instance over any_instance.expects

* fix CodeRabbit feedback - Reusing the same stub for both classifications hides a contract mismatch

* fix CodeRabbit FEEDBACK - Reconsider enabling Skylight by default in development

* fix CodeRabbitAI FEEDBACK - reconsider unconditionally enabling Skylight in development

* fix Security scan FEEDBACK before PR merge

* fix jjmata feedback

test/controllers/pages_controller_test.rb

@@ -14,6 +14,39 @@ class PagesControllerTest < ActionDispatch::IntegrationTest
     assert_response :ok
   end
 
+  test "dashboard memoizes income statement period totals while rendering" do
+    income_statement = IncomeStatement.new(@family)
+    IncomeStatement.stubs(:new).returns(income_statement)
+
+    fake_expense_period_total = IncomeStatement::PeriodTotal.new(
+      classification: "expense",
+      total: 0,
+      currency: @family.currency,
+      category_totals: []
+    )
+
+    fake_income_period_total = IncomeStatement::PeriodTotal.new(
+      classification: "income",
+      total: 0,
+      currency: @family.currency,
+      category_totals: []
+    )
+
+    income_statement.expects(:build_period_total)
+      .with(classification: "expense", period: kind_of(Period))
+      .once
+      .returns(fake_expense_period_total)
+
+    income_statement.expects(:build_period_total)
+      .with(classification: "income", period: kind_of(Period))
+      .once
+      .returns(fake_income_period_total)
+
+    get root_path
+
+    assert_response :ok
+  end
+
   test "intro page requires guest role" do
     get intro_path