Add test coverage for comix coverFromPage()

Extend the test harness's document stub with a querySelectorAll("img[alt]")
fake (module-level pageImages fixture, mirroring metaTags), then assert on
p.cover for a matching alt and for no match. Previously the guard in
coverFromPage() always short-circuited under test since querySelectorAll
didn't exist on the stub, so the alt-matching loop had zero coverage.

userscript/test/logic.test.js

@@ -31,6 +31,9 @@ globalThis.location = {
 
 // og: meta tags the adapters read through meta(). Reassigned per test.
 let metaTags = {};
+// img[alt] elements comix's coverFromPage() scans. Reassigned per test; each
+// entry is {alt, src}.
+let pageImages = [];
 globalThis.document = {
   querySelector(sel) {
     const m = sel.match(/^meta\[property="([^"]+)"\]$/);
@@ -38,6 +41,12 @@ globalThis.document = {
     const v = metaTags[m[1]];
     return v == null ? null : { getAttribute: () => v };
   },
+  querySelectorAll(sel) {
+    if (sel !== "img[alt]") return [];
+    return pageImages.map((img) => ({
+      getAttribute: (attr) => img[attr] ?? null,
+    }));
+  },
   addEventListener() {},
   body: undefined,
 };
@@ -214,6 +223,26 @@ test("comix parses decimal chapter numbers", () => {
   assert.equal(p.chapterNum, 80.5);
 });
 
+test("comix.detect reads the cover from an img whose alt matches the cleaned title", () => {
+  metaTags = { "og:title": "Dungeons and Crayons · Ch.80" };
+  pageImages = [
+    { alt: "Some Other Series", src: "https://cdn.example/other.jpg" },
+    { alt: "Dungeons and Crayons", src: "https://cdn.example/cover.jpg" },
+  ];
+  const p = comix.detect(
+    loc("https://comix.to/title/n8we-dungeons-and-crayons/11139891-chapter-80")
+  );
+  assert.equal(p.cover, "https://cdn.example/cover.jpg");
+});
+
+test("comix.detect leaves cover empty when no img alt matches the title", () => {
+  metaTags = { "og:title": "Dungeons and Crayons" };
+  pageImages = [{ alt: "Some Other Series", src: "https://cdn.example/other.jpg" }];
+  const p = comix.detect(loc("https://comix.to/title/n8we-dungeons-and-crayons"));
+  assert.equal(p.cover, "");
+  pageImages = [];
+});
+
 test("comix ignores unrelated paths", () => {
   assert.equal(comix.detect(loc("https://comix.to/browse")).type, "other");
 });