Fill in the seed project status document

[rxdt]

Goal

Replace the placeholders in docs/PROJECT_STATUS.md with a short, accurate status for the current template.

Scope

• Summarize the current seed app and harness state.
• List the current gate command.
• Keep the file under 100 lines, matching its own instruction.

Acceptance criteria

• No placeholder bullets remain in docs/PROJECT_STATUS.md.
• The status reflects the current repo, not future work.
• pnpm gate passes.