Your board, in its current form, is not ready for that yet. If you want to deploy sketches directly from the Arduino IDE to your custom board, then it must have at a minimum:
- The arduino bootloader loaded on to the AVR
- Some kind of way to accept UART (serial) communications from the PC. (serial cable with max232 level shifter, or a usb to serial chip like the FT232)
The arduino bootloader is a program that is loaded on to the board from the factory. It is the one that is responsible for accepting new programs ("sketches") from the IDE over serial communication with the PC and writes the program to a particular location on the chip where it will then run that application.
So how did the bootloader get there in the first place? It's written there using a tool called an ISP programmer. There are plenty of them out there to choose from but they all do the same thing: they follow a protocol to put the chip into a programming mode and then writes directly to its flash memory. If you want to get the arduino bootloader on to your blank AVR then you'll have to do this and also get familiar with a command line tool called
avr-dude. As others have pointed out, you can actually make your own ISP programmer from an existing arduino because all you need it to do is follow that programming protocol - which is well documented and can be implemented by writing your own sketch to do that.
Since you don't want to buy any more external hardware, perhaps the best way is to buy an AVR chip with the arduino bootloader already loaded on to it as another answer suggested. This still leaves point #2 - you'll need to find a way to hook up your PC to your board. There's no getting around the fact that you'll need some kind of cable or IC or combination of both to get that done.