fonts: add Simplified Chinese font support

[mydanyi]

Summary

Add Noto Sans CJK SC to the ROCKNIX image so Simplified Chinese text is available to fontconfig applications such as Steam and to EmulationStation.

• package the upstream Noto Sans CJK SC 2.004 regular font
• install it in /usr/share/fonts for system-wide fontconfig discovery
• use it as EmulationStation's CJK fallback without storing a second copy
• select it for the default theme when the language is Chinese

Testing

• all changed package scripts pass bash -n
• the upstream font matches the configured SHA256
• fc-query identifies the font as Noto Sans CJK SC with zh-cn support and CJK Unified Ideographs coverage
• the generated Chinese theme override parses as valid XML
• git diff --check passes
• a full image build and on-device test have not been run yet

Additional Context

The source OTF is 16,437,364 bytes; compressed image impact has not been measured. The EmulationStation fallback is a symlink to avoid embedding the font twice.

This follows up #3177 and ROCKNIX/emulationstation-next#28. Related earlier font proposals: #2875 and #2880.

@loki666 @spycat88

---

AI Usage

Did you use AI tools to help write this code? PARTIALLY

[mydanyi]

@spycat88 @loki666

I recently published a Bilibili video demonstrating ROCKNIX running on the newly supported AYANEO Pocket S Mini:

https://www.bilibili.com/video/BV1FR8k6hEK7

It has reached 8,937 views and 108 comments so far, showing meaningful interest in ROCKNIX from Chinese-speaking handheld users. At the moment, selecting Simplified Chinese without a CJK font still leaves missing-glyph boxes in EmulationStation and Steam, so the localization is not fully usable.

When you have time, I would appreciate a review of this PR. It would complete the Chinese user experience alongside ROCKNIX/emulationstation-next#28. Thank you.