docs(repo): add contributor orientation guides

[horacioh]

Summary

• Add a canonical Seed Builder Guide with read order, repo map, doc status conventions, and workflow entry points.
• Add architecture, code map, domain glossary, dev setup, and feature brief docs for cross-subsystem contributor orientation.
• Add backend and frontend subsystem READMEs covering package ownership, sources of truth, and common commands.
• Refresh existing README and agent/editor command docs to use current pnpm, web, and repo workflow guidance.

Breaking Changes

None.

[burdiyan]

If this is for agents, why is it in the README.md and not in AGENTS.md?

On the other hand:

I'm not a big fan of listing files and directories in markdown files, because it often confuses the agent when stuff changes and document goes stale. And even if it stays up to date, it would often hallucinate something because it would rely on the docs instead of checking the actual code.

In my experience with Claude, Codex, and Kimi, no amount of asking to keep docs up to date reliably keeps them up to date.

The code itself + per-folder AGENTS.md when necessary works pretty good for me. Some additional tools that would index the code and search for it more quickly also help:

1. https://github.com/dmtrKovalenko/fff
2. https://github.com/glommer/memelord
3. https://github.com/tobi/qmd
4. There's lots of them...

[burdiyan]

Same comment here: I'm very reluctant to duplicating stuff that's already clear from the file-system layout into markdown files.

This file in particular looks very overwhelming. I can't see how this could help us save tokens or drive the agent better. I wouldn't be surprised if it was actually harming — causing the agent to read unnecessary files, and blowing up the context window with irrelevant information.