Fix duplicate marketplace categories caused by case-sensitive displayName matching (#7334)

Category.merge() and findOrCreateCategory() used equals() to match categories
by displayName, causing "AI" and "ai" to be treated as distinct categories.
This resulted in duplicate category entries on the marketplace page when
different recipe modules used different casing for the same category name
(e.g. rewrite-java uses "AI" while rewrite-ai uses "ai").

Switch both methods to equalsIgnoreCase() so categories with the same name
but different casing are properly merged. The first-seen casing is preserved.

Author: pdelagrave

rewrite-core/src/main/java/org/openrewrite/marketplace/RecipeMarketplace.java

@@ -79,7 +79,7 @@ public void merge(Category category) {
             for (Category subCategory : category.categories) {
                 Category existingSubCategory = null;
                 for (Category c : categories) {
-                    if (c.getDisplayName().equals(subCategory.getDisplayName())) {
+                    if (c.getDisplayName().equalsIgnoreCase(subCategory.getDisplayName())) {
                         existingSubCategory = c;
                         break;
                     }
@@ -154,7 +154,7 @@ public void install(RecipeListing recipe, List<CategoryDescriptor> categoryPath)
 
         private Category findOrCreateCategory(CategoryDescriptor categoryDescriptor) {
             for (Category category : categories) {
-                if (category.getDisplayName().equals(categoryDescriptor.getDisplayName())) {
+                if (category.getDisplayName().equalsIgnoreCase(categoryDescriptor.getDisplayName())) {
                     return category;
                 }
             }

rewrite-core/src/test/java/org/openrewrite/marketplace/RecipeMarketplaceReaderTest.java

@@ -436,6 +436,50 @@ void mergePreservesMetadata() {
         assertThat(mergedOther.getMetadata().get("embedding")).isEqualTo("xyz789");
     }
 
+    @Test
+    void mergeCategoriesCaseInsensitive() {
+        // Simulates the real-world scenario where rewrite-java defines category "AI"
+        // and rewrite-ai defines category "ai" -- these should merge into one category
+        RecipeMarketplace marketplace1 = new RecipeMarketplaceReader().fromCsv("""
+          name,category1,ecosystem,packageName
+          org.openrewrite.java.ai.ClassDefinitionLength,AI,maven,org.openrewrite:rewrite-java
+          org.openrewrite.java.ai.MethodDefinitionLength,AI,maven,org.openrewrite:rewrite-java
+          """);
+
+        RecipeMarketplace marketplace2 = new RecipeMarketplaceReader().fromCsv("""
+          name,category1,ecosystem,packageName
+          io.moderne.ai.FindAgentsInUse,ai,maven,io.moderne.recipe:rewrite-ai
+          io.moderne.ai.FindLibrariesInUse,ai,maven,io.moderne.recipe:rewrite-ai
+          """);
+
+        marketplace1.getRoot().merge(marketplace2.getRoot());
+
+        assertThat(marketplace1.getRoot().getCategories())
+          .as("AI and ai should merge into a single category")
+          .hasSize(1);
+        assertThat(marketplace1.getRoot().getCategories().getFirst().getRecipes()).hasSize(4);
+        // The first-seen casing wins
+        assertThat(marketplace1.getRoot().getCategories().getFirst().getDisplayName()).isEqualTo("AI");
+    }
+
+    @Test
+    void installCategoriesCaseInsensitive() {
+        // When installing recipes via CSV where one uses "AI" and another uses "ai"
+        // in the same category position, they should land in the same category
+        RecipeMarketplace marketplace = new RecipeMarketplaceReader().fromCsv("""
+          name,category1,ecosystem,packageName
+          org.example.Recipe1,AI,maven,org.example:test1
+          org.example.Recipe2,ai,maven,org.example:test2
+          """);
+
+        assertThat(marketplace.getRoot().getCategories())
+          .as("AI and ai should be treated as the same category during install")
+          .hasSize(1);
+        assertThat(marketplace.getRoot().getCategories().getFirst().getRecipes()).hasSize(2);
+        // The first-seen casing wins
+        assertThat(marketplace.getRoot().getCategories().getFirst().getDisplayName()).isEqualTo("AI");
+    }
+
     private static RecipeMarketplace.Category findCategory(RecipeMarketplace.Category category, String name) {
         return category.getCategories().stream()
           .filter(c -> c.getDisplayName().equals(name))