fix(CQ-API-7): Fix N+1 query in knowledge tag lookup

Replace Promise.all of individual findUnique queries per tag with a
single findMany batch query. Only missing tags are created individually.
Tag associations now use createMany instead of individual creates.
Also deduplicates tags by slug via Map, preventing duplicate entries.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/api/src/knowledge/knowledge.service.ts

@@ -821,45 +821,48 @@ export class KnowledgeService {
       return;
     }
 
-    // Get or create tags
-    const tags = await Promise.all(
-      tagNames.map(async (name) => {
-        const tagSlug = this.generateSlug(name);
+    // Build slug map: slug -> original tag name
+    const slugToName = new Map<string, string>();
+    for (const name of tagNames) {
+      slugToName.set(this.generateSlug(name), name);
+    }
+    const tagSlugs = [...slugToName.keys()];
 
-        // Try to find existing tag
-        let tag = await tx.knowledgeTag.findUnique({
-          where: {
-            workspaceId_slug: {
-              workspaceId,
-              slug: tagSlug,
-            },
-          },
-        });
+    // Batch fetch all existing tags in a single query (fixes N+1)
+    const existingTags = await tx.knowledgeTag.findMany({
+      where: {
+        workspaceId,
+        slug: { in: tagSlugs },
+      },
+    });
 
-        // Create if doesn't exist
-        tag ??= await tx.knowledgeTag.create({
+    // Determine which tags need to be created
+    const existingSlugs = new Set(existingTags.map((t) => t.slug));
+    const missingSlugs = tagSlugs.filter((s) => !existingSlugs.has(s));
+
+    // Create missing tags
+    const newTags = await Promise.all(
+      missingSlugs.map((slug) => {
+        const name = slugToName.get(slug) ?? slug;
+        return tx.knowledgeTag.create({
           data: {
             workspaceId,
             name,
-            slug: tagSlug,
+            slug,
           },
         });
-
-        return tag;
       })
     );
 
-    // Create tag associations
-    await Promise.all(
-      tags.map((tag) =>
-        tx.knowledgeEntryTag.create({
-          data: {
-            entryId,
-            tagId: tag.id,
-          },
-        })
-      )
-    );
+    const allTags = [...existingTags, ...newTags];
+
+    // Create tag associations in a single batch
+    await tx.knowledgeEntryTag.createMany({
+      data: allTags.map((tag) => ({
+        entryId,
+        tagId: tag.id,
+      })),
+    });
   }
 
   /**