README: TinyTang's prefix is tang

[aquasock]

Records TinyTang's prefix, tang, in the Community ports table, as STANDARDS.md asks, and updates its notes to what the port does now.

• What changes for users: documentation only, one row of the README. No commands, options, API or board keys change.
• Platforms: no code change. TinyTang runs on the BL616 of the Sipeed Tang Console 138K, built against TinyDesk Shell and TinyDesk v0.1.5; its README now states the platform, versions, prefix, additions, omissions and licence that STANDARDS.md lists for community ports.
• Tests: the host tests pass (8 of 8) with no build warnings.

🤖 Generated with Claude Code

[aquasock]

Created in error by AI agent. New PR to replace.
RC: AI miscommunication/user error.
I think I was tired, I suspect the "Generated with Claude Code " was the agent being hesitant and wanted to flag it for me just in case it was really what I intended to do. It would explain the next PR not having the tag as well. I think the agent then assumed it was safe to speak in my voice from then on going forward and automatically push PRs as dev work continued. None of this is acceptable.
Resolution: New core.md rule for agents forbidding them from pushing anything to any repository other than those under the username of "aquasock". (515969c) (7cf9ede) Will continue dev work and monitor.