docs(roadmap): rewrite around open problems and preliminary ideas

[ignorejjj]

What

Rewrites the roadmap (EN + ZH) as a few categories of open problems, each paired with the team's current preliminary thinking, in a leaner and more restrained voice.

Reorganized into three directions:

• Core capability — long-horizon process management, idea-quality assessment (critic role), self-evolution (trajectory export → reusable skills/experience), composite optimization objectives (rubric / LLM-judge / multi-objective, with comparability + anti-gaming), stronger agentic research ability.
• External resources — stateful long-horizon environments (e.g. office agent harnesses), automated environment collection.
• User experience — a worked-examples gallery, better single-run export/comparison.

Why

The previous roadmap read as a prescriptive feature list. Framing it as open questions + preliminary ideas is more honest for a research project and lowers the bar for contributors to pick up a thread.

Notes

• docs/roadmap.md (EN) and docs/roadmap.zh.md (ZH) kept in sync.
• No code changes; docs only. No internal links pointed at the old section anchors (checked), so nothing breaks.
• Rendered locally with mkdocs serve (i18n EN/ZH) — builds clean.