Add LineItem CSV import and fix Unit API

database/migrations/2025_09_18_193251_create_line_items_table.php

@@ -18,10 +18,13 @@ public function up(): void
             $table->boolean('is_section')->default(false);
             $table->string('title')->nullable();
             $table->string('description')->nullable();
-            $table->integer('quantity')->default(1);
+            $table->decimal('quantity')->default(1);
             $table->foreignId('unit_id')->nullable()->constrained()->nullOnDelete();
             $table->decimal('price', 10, 2)->nullable();
             $table->timestamps();
+
+            $table->index('position');
+            $table->index('invoice_id');
         });
     }