Connect CalDAV todos to DB-Items, finish todo component and add it to pipeline items

database/migrations/2025_11_28_000000_create_todo_table.php

@@ -22,6 +22,9 @@ public function up(): void
             $table->timestamp('last_modified')->nullable(); // iCal LAST-MODIFIED
             $table->string('parent')->nullable()->index(); // RELATED-TO (parent UID)
             $table->string('object')->nullable(); // RELATED-TO (object reference)
+            $table->unsignedBigInteger('todoable_id');
+            $table->string('todoable_type');
+            $table->index(['id', 'todoable_id', 'todoable_type']);
         });
     }