Fix GCC build and add MAG274QRF-QD (3CC2) support

[aydiler]

Summary

• Fix build failure with GCC 14+ by adding missing #include <cstdint> to psteelseries.h
• Add support for MAG274QRF-QD (3CC2) variant with hardware identifier 0x9a

Details

Build Fix

psteelseries.h uses uint8_t without including <cstdint>. Newer GCC versions are stricter about implicit includes and fail to compile:

src/psteelseries.h:22:32: error: expected ')' before 'n'
   22 |         steel_rgb_entry(uint8_t n, uint8_t vr, uint8_t vg, uint8_t vb)

Monitor Support

Adds support for MAG274QRF-QD monitors manufactured in late 2023 with variant code 3CC2. These units report identifier 00\x9a instead of 00e but use the same V56 firmware.

Monitor info:

• Model: MAG274QRF-QD
• Variant: 3CC2
• Manufactured: 2023.11
• Identifier: 00\x9a
• Firmware version: V56

Debug output:

Vendor Id:      0x1462
Product Id:     0x3fa4
Product:        MSI Gaming Controller
Monitor Series: MAG274QRF-QD (3CC2)
LED support:    MysticOptix

Test plan

• Verified build fails without cstdint fix on GCC 14
• Verified monitor is detected as "Unknown" without the variant entry
• Verified brightness/contrast read and write works with the patch
• Verified MysticOptix LED control is available

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