Complete the USB Flashlight tutorial

[thisisharsh7]

The Building a Simple USB Flashlight tutorial currently feels incomplete compared with the other tutorials.

It only includes a short overview and one embedded final circuit preview. It does not walk through the build step by step or explain the circuit parts. Could use the same flow as the other tutorials: introduce the parts, build the circuit step by step, and end with the final preview notes.

Happy to work on this.

[justact04]

/attempt #555

[pxtung299-bot]

Hi! I've opened PR #597 to complete this tutorial. It follows the same step-by-step structure as the other tutorials with a full code example, circuit explanation, and verification checklist. Happy to revise anything!

[BossChaos]

🎯 Completing this tutorial! PR: #604

Expanded from 42 lines to 326 lines with complete circuit theory, step-by-step TSX construction, PCB layout guide, cost analysis, and extensions. Wallet: 0xdaE5d307339074A24F579dB48e7c639359D94904