Roadmap: rewrite docs and roadmap around first-class coding-agent milestones

[Hmbown]

Summary

The current handoff/todo material is too weighted toward local UI polish. We need a clearer public roadmap that explains how deepseek-tui becomes a first-class coding agent while keeping DeepSeek’s whale identity and plain-language coherence story front and center.

Scope

• Rewrite the roadmap/handoff docs around product-level milestones instead of isolated UI tickets
• Update README/AGENTS/docs to explain:
  • what makes deepseek-tui different
  • how coherence is presented in plain language
  • how runtime/API/safety/extensions fit together
• Keep the tone practical and accessible for contributors picking up the next issue

Acceptance Criteria

• The roadmap reflects platform, safety, eval, ecosystem, and UX priorities rather than only polish tasks
• Coherence is described in plain language, not math-heavy language
• Contributors can quickly understand where the project is headed and why
• Major docs no longer contradict the current architecture and migration status

Starting Points

• README.md
• AGENTS.md
• AI_HANDOFF.md
• todo.md
• docs/ARCHITECTURE.md
• docs/workspace_migration_status.md

[Hmbown]

Closing as stale — these April 11 roadmap items predate the v0.4.x / v0.5.0 work and are being replaced by concrete, actionable issues (#28-#35). Will reopen specific items if/when they're picked up.