docs: move NEXT_STEPS.md to docs/ROADMAP.md

[devin-ai-integration]

Summary

git mv NEXT_STEPS.md docs/ROADMAP.md — the roadmap now sits with the rest of the docs instead of the repo root, retitled "Systemica — Roadmap" and linked from docs/README.md under Implementation Status. The stale "plus this branch" in its baseline line is dropped, since the file is no longer branch-local. Content is otherwise unchanged.

References updated to the new path: the python-test comment in .circleci/config.yml and the two §P1/§P2 citations in .agents/skills/testing-sysml-repl/SKILL.md.

Separately (not in this diff), the roadmap's content was ingested into repo-pinned Devin knowledge notes — release follow-through R1–R4, the pysysml/gRPC gaps, the Track A backlog, the REPL and coverage items, the gate baseline and batch-partitioning lessons — and the corpus-baseline note was refreshed from 71/100 to the 98/100 ceiling.

Link to Devin session: https://nasa-jpl-demo.devinenterprise.com/sessions/67a567f1cba64beba7ffd67172d77567
Requested by: @HuiJun

[devin-ai-integration]

Original prompt from jason.han

@JPL-Devin/Systemica Look at NEXT_STEPS.md in this repo. That file should never have been committed, but it does contain what we want to do next. Can we ingest that file and then remove it from the repo?

[devin-ai-integration]

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

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