docs(dev_board): add ArtInChip D121BBV-HMI-DEMO certified board

[tanghao-xiaomi]

Summary

Adds the ArtInChip D121BBV-HMI-DEMO board to the openvela compatibility-certified
board list, in both the Chinese and English pages.

Field	Value
Board	D121BBV-HMI-DEMO
Manufacturer	ArtInChip
Chip model	D121BBV (RISC-V)
Certified version	openvela 5.4
Certificate	No. OV20260731002

Changes

• zh-cn/dev_board/Certified_Board.md / en/dev_board/Certified_Board.md: new table row for the board.
• Board photo and compatibility certificate images added under each language's own dev_board/images/ directory.
• The English page now references images from en/dev_board/images/ instead of pointing into the Chinese directory, so each language version is self-contained.

Verification

• All four image references in each page resolve to files that exist in that page's own images/ directory; no cross-language image references and no dead links remain.
• The chip model D121BBV matches the board name printed on the compatibility certificate.
• The Chinese and English tables have identical row and column structure, and the cross-language switch links still point at the corresponding language version.