Add theme-aware ATTENTRIX README lockup

[CodingIsCool666]

Summary

• place the ATTENTRIX wordmark to the right of the emblem in the README header
• use a white wordmark for GitHub dark mode and a navy wordmark for light mode
• generate both lockups reproducibly from the tracked brand assets
• approve only these two new PNGs in the public export policy

Verification

• 866 Python tests pass
• public repository policy passes with 709 approved files
• clean snapshot manifest reports zero findings
• generated lockups were visually inspected at full resolution