app: Generate All says so when every scene is excluded

Found by the adversarial pass on the exclude commit: every other
early-return in generateAll() says something (empty load, cancelled,
N failed) except this one -- excluding every scene made the button do
nothing with no feedback, indistinguishable from a hang.

app/boot.js

@@ -151,7 +151,7 @@ async function start() {
     // 5" while two of the five were never going to run reads as a wrong
     // number, not as a batch that respected the exclude.
     const scenes = project.scenes.filter((s) => !s.excluded);
-    if (!scenes.length) return;
+    if (!scenes.length) { page.transport.say("Every scene is excluded -- nothing to generate."); return; }
     generateAllBtn.setDisabled(true);
     batchCancelled = false;
     page.transport.hold(`Generating scene 1 of ${scenes.length}…`);

app/tests-layout/generate_all.spec.js

@@ -87,6 +87,24 @@ test("an excluded scene is skipped, and does not count toward the total", async
     .toBeVisible({ timeout: 15000 });
 });
 
+test("excluding every scene says so instead of doing nothing silently", async ({ page }) => {
+  await app(page);
+  await page.evaluate(() => {
+    const { project } = window.FunPack;
+    while (project.scenes.length < 2) project.addScene();
+    for (const s of project.scenes) project.setScene(s.id, "excluded", true);
+  });
+
+  const btn = page.getByRole("button", { name: "Generate All" });
+  await btn.click();
+
+  await expect(page.locator(".cx-panel-status", { hasText: /every scene is excluded/i }))
+    .toBeVisible();
+  // Nothing was ever started -- the button was never disabled by a batch
+  // that had nothing to run.
+  await expect(btn).toBeEnabled();
+});
+
 test("a second click while a batch is already running does not start an overlapping one", async ({ page }) => {
   await app(page);
   await page.evaluate(() => {