Add Stock Tracking endpoint to Inventory

Adds GET /client/inventory/stock-movements, a unified read-only ledger
flattening every GRN line, sale line and return across all products
into one shape for the new Stock Tracking tab's table.

Controllers/InventoryController.cs

@@ -170,5 +170,12 @@ namespace Fitness_core_BE.Controllers
                 notes = request.Notes,
                 returnedAt = request.ReturnedAt?.ToString("o")
             }, HttpContext));
+
+        [CustomMiddleware]
+        [TenantResolution]
+        [RequiresPermission("inventory")]
+        [HttpGet("stock-movements")]
+        public async Task<ActionResult<ApiResponse<object>>> GetStockMovements()
+            => Response(await _inventoryService.GetStockMovements(new { }, HttpContext));
     }
 }