Force tags to be lowercase in the frontend during parsing

The backend already enforces lowercase of the tags, but the frontend did not.
This could result in double challenge imports if you parse again.
Now after the custom parser, all tags are forced to be lower case and unique.

This fixes #89

front/src/components/Dialogs/TaskImportDialog.vue

@@ -175,29 +175,33 @@ export default defineComponent({
     onPaste() {
       void this.$nextTick(() => this.autoDetectParser());
     },
+    normalizeTags(tags: string[]): string[] {
+      if (tags.length == 0) return [];
+      return Array.from(new Set(tags.map((t) => t.trim().toLowerCase())));
+    },
     parseTasks(v: string): ParsedTask[] {
       // Get list of task {title,category} from parse
       const parsedTasks = this.currentParser.value.parse(v);
       // Precompute a set of task to avoid N square operation
       const hashTask = (title: string, tags: string[]): string =>
-        title +
-        tags
-          .map((t) => t.toLowerCase())
-          .sort()
-          .join('');
+        title + this.normalizeTags(tags).sort().join('');
       const taskSet = new Set();
       for (const task of this.ctf.tasks) {
         taskSet.add(
           hashTask(
             task.title,
-            task.assignedTags.map((t) => t.tag)
+            this.normalizeTags(task.assignedTags.map((t) => t.tag))
           )
         );
       }
       // mark already existing tasks
       return parsedTasks.map((task) => {
         const hash = hashTask(task.title, task.tags);
-        return { ...task, keep: !taskSet.has(hash) };
+        return {
+          ...task,
+          tags: this.normalizeTags(task.tags),
+          keep: !taskSet.has(hash),
+        };
       });
     },
     computeTags(tags: { nodeId: number; tag: string }[]) {