chore: bootstrap Spec Kit workflow for Wiii

[meiiie]

Summary

Bootstrap Spec Kit for Wiii so architecture-sensitive and multi-agent work has a shared constitution, specification, planning, task, and implementation workflow.

Scope

• Initialize Spec Kit v0.8.7 Codex skills mode for this repository.
• Track only .agents/skills/speckit-* while keeping existing local .agents/skills/* ignored.
• Add a Wiii-specific constitution for native runtime ownership, living memory safety, streaming-first UX, safe tools/host control, and multi-agent change discipline.
• Document when and how Wiii agents should use Spec Kit.

Non-goals

• No runtime behavior changes.
• No LangChain/LangGraph cleanup implementation in this PR.
• No changes to backend, desktop, provider, memory, RAG, Pointy, or LMS code.

Verification

• PYTHONIOENCODING=utf-8 PYTHONUTF8=1 specify check
• git diff --check