Add negative assertions and selector_count to DOMTest

Component tests keep needing to assert that something is NOT on the
page (a closed panel, a cleared list), and until now every consuming
app hand-rolled querySelectorAll counting through JS.eval. DOMTest
gains assert_no_selector / assert_no_text as the natural counterparts
of the existing assertions, plus selector_count for cardinality
checks.

Verified against the tsunematsu app's picotest suite (76 tests).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: hasumikin

lib/funicular/testing/node_runner.mjs

@@ -105,6 +105,15 @@ module Funicular
         report(!actual.nil?, "Expected selector #{selector.inspect} to exist", selector, actual)
       end
 
+      def assert_no_selector(selector)
+        actual = query(selector)
+        report(actual.nil?, "Expected selector #{selector.inspect} to be absent", selector, actual)
+      end
+
+      def selector_count(selector)
+        JS.eval("document.querySelectorAll(" + JSON.generate(selector) + ").length").to_i
+      end
+
       def text(selector = nil)
         target = selector ? query(selector) : document.body
         target ? target[:textContent].to_s : ''
@@ -120,6 +129,16 @@ module Funicular
         )
       end
 
+      def assert_no_text(expected, selector = nil)
+        actual = text(selector)
+        report(
+          !actual.include?(expected.to_s),
+          "Expected text not to include #{expected.to_s.inspect}",
+          expected.to_s,
+          actual
+        )
+      end
+
       def dispatch(selector, event_type)
         script = "document.querySelector(" + JSON.generate(selector) + ")" \
           + ".dispatchEvent(new Event(" + JSON.generate(event_type) \