fix(cli): contrast gate judges only readable content; examples pass check

Three filters keep the escalated contrast gate honest, each surfaced by
running check across the registry examples:
- data-layout-ignore (the layout audit's existing decorative opt-out)
  now also excludes set-dressing text from the contrast audit — one
  vocabulary for 'not copy a viewer must read'.
- Text that has (nearly) left the canvas is skipped: sampling a clamped
  off-canvas box reads border pixels and produced the classic false
  white-on-white (a cursor exiting the frame).
- Contrast failures follow the same persistence rule as layout findings:
  observed at a single sample of a multi-sample sweep demotes to
  warning; held failures gate.

Example fixes the sweep exposed: motion-blur's 21 deliberately-dim rail
labels are marked decorative (its vivid labels pass on their own);
nyt-graph's subtitle and source-note adopt the gate's suggested
compliant gray; decision-tree's declared duration drops 15s to 10s —
its content ends at ~9.5s and every render shipped a blank white tail.

packages/cli/src/utils/checkBrowser.test.ts

@@ -51,6 +51,18 @@ afterEach(() => {
   Reflect.deleteProperty(window, "__contrastAuditRestoreIfPending");
 });
 
+function installSessionMock(page: ReturnType<typeof fakePage>): void {
+  const browser = Object.assign(Object.create(null), {
+    close: vi.fn(async () => undefined),
+  });
+  vi.mocked(openSettledCompositionPage).mockImplementation(
+    async (_html: string, _url: string, options: OpenSettledCompositionPageOptions) => {
+      await options.beforeNavigate?.(page);
+      return { page, browser, renderReadyTimedOut: false };
+    },
+  );
+}
+
 it("carries raw browser geometry through the page driver and pipeline", async () => {
   vi.spyOn(Date, "now")
     .mockReturnValueOnce(100)
@@ -68,15 +80,7 @@ it("carries raw browser geometry through the page driver and pipeline", async ()
   Object.defineProperty(window, "innerHeight", { configurable: true, value: 360 });
   installRects();
   const page = fakePage();
-  const browser = Object.assign(Object.create(null), {
-    close: vi.fn(async () => undefined),
-  });
-  vi.mocked(openSettledCompositionPage).mockImplementation(
-    async (_html: string, _url: string, options: OpenSettledCompositionPageOptions) => {
-      await options.beforeNavigate?.(page);
-      return { page, browser, renderReadyTimedOut: false };
-    },
-  );
+  installSessionMock(page);
 
   const result = await runBrowserCheck(
     PROJECT,
@@ -184,15 +188,7 @@ it("round-trips the browser script's raw contrast candidates back into finish",
     }
   });
   page.screenshot = vi.fn(async () => "c3R1Yg==");
-  const browser = Object.assign(Object.create(null), {
-    close: vi.fn(async () => undefined),
-  });
-  vi.mocked(openSettledCompositionPage).mockImplementation(
-    async (_html: string, _url: string, options: OpenSettledCompositionPageOptions) => {
-      await options.beforeNavigate?.(page);
-      return { page, browser, renderReadyTimedOut: false };
-    },
-  );
+  installSessionMock(page);
 
   await runBrowserCheck(
     PROJECT,