fix: update examples for current M5 library APIs

[LuoIsHere]

Description

Update DLight example sketches to use M5Unified display APIs.

This replaces the separate M5GFX display instance with the unified M5.Display object provided by M5Unified, avoiding multiple display objects in the same sketch and aligning the examples with the current M5Stack application-layer API style.

Changes

• Replace legacy board-specific display includes with M5Unified.h
• Use M5Canvas canvas(&M5.Display) for display examples
• Remove separate M5GFX display instances and display.begin()
• Use M5.Display.width() / M5.Display.height() when creating sprites
• Move StickC display rotation to M5.Display.setRotation(3)
• Update Atom example from M5Atom display API to M5Unified with Adafruit_NeoPixel
• Keep existing Unit and HAT DLight sensor initialization logic unchanged

Notes

• Atom example requires the Adafruit NeoPixel library:
  https://github.com/adafruit/Adafruit_NeoPixel

Test

• Verified all updated examples compile successfully.