docs(q8b): document 50-pin B2B connector - #2175

Summary

• Document the 50-Pin B2B connector and PCIe / MIPI CSI / I2C support in the Chinese and English Dragon Q8B specifications.
• Update the product and hardware interface tables to match labels 1-23 in the new illustration.

Why

The existing specifications omit this connector, and the interface tables use numbering from the previous illustration. The matching image update is submitted separately as a shared asset change.

Verification

• Checked each entry against the supplied annotated interface image, including label 13 on the rear and subsequent labels through 23.
• Ran pre-commit run --files on the four paired documents and both assets.
• Local PR guard: one product scope, four files, both languages paired, no reasons.