chore: drop asuracomic.net from the userscript, CORS allowlist and docs (#96)

The old domain's deep links 301 to the asurascans.com root, discarding the
path, so a page on it never yields a series document and a stored address on
it never yields a series page. #94 pinned each Site to one hostname, which
already rejects such an address server-side; this removes the remaining
references so nothing invites a Reader onto the dead host.

Live deploys still carry the origin in their own .env and must drop it there
too - the allowlist is read from the environment, not from these defaults.

backend/api_test.go

@@ -33,7 +33,7 @@ const testCoverBaseURL = "https://bookmarks.test"
 func testConfig() Config {
 	return Config{
 		TokenKey:       testTokenKey,
-		AllowedOrigins: []string{"https://asuracomic.net", "https://demonicscans.org"},
+		AllowedOrigins: []string{"https://asurascans.com", "https://demonicscans.org"},
 		Port:           "8080",
 	}
 }
@@ -169,7 +169,7 @@ func TestAuthAccepted(t *testing.T) {
 func TestCORSPreflight(t *testing.T) {
 	srv := newTestServer(t)
 	req := httptest.NewRequest(http.MethodOptions, "/bookmarks/asura:foo-1", nil)
-	req.Header.Set("Origin", "https://asuracomic.net")
+	req.Header.Set("Origin", "https://asurascans.com")
 	req.Header.Set("Access-Control-Request-Method", "PUT")
 	rr := httptest.NewRecorder()
 	srv.ServeHTTP(rr, req)
@@ -177,7 +177,7 @@ func TestCORSPreflight(t *testing.T) {
 	if rr.Code != http.StatusNoContent {
 		t.Fatalf("preflight status = %d, want 204", rr.Code)
 	}
-	if got := rr.Header().Get("Access-Control-Allow-Origin"); got != "https://asuracomic.net" {
+	if got := rr.Header().Get("Access-Control-Allow-Origin"); got != "https://asurascans.com" {
 		t.Fatalf("Allow-Origin = %q, want reflected origin", got)
 	}
 	if got := rr.Header().Get("Access-Control-Allow-Methods"); got == "" {
@@ -204,11 +204,11 @@ func TestBookmarkRoundTrip(t *testing.T) {
 	key := "asura:solo-leveling-123"
 	in := store.Bookmark{
 		Title:          "Solo Leveling",
-		SeriesURL:      "https://asuracomic.net/series/solo-leveling-123",
-		Cover:          "https://asuracomic.net/cover.jpg",
+		SeriesURL:      "https://asurascans.com/series/solo-leveling-123",
+		Cover:          "https://asurascans.com/cover.jpg",
 		LastChapter:    "Chapter 10",
 		LastChapterNum: 10,
-		LastChapterURL: "https://asuracomic.net/series/solo-leveling-123/chapter/10",
+		LastChapterURL: "https://asurascans.com/series/solo-leveling-123/chapter/10",
 	}
 	body, _ := json.Marshal(in)