docs(oat): harden HiLL prompts and artifact tracking

[tkstang]

Purpose

Tighten OAT implementation/quick-start instructions so implementation checkpoint prompts are more explicit and quick-start artifact changes are persisted before pauses or handoff.

Changes

• require oat-project-implement to always summarize every plan phase, state total phase count/final phase ID, and present an explicit 3-option checkpoint choice
• document the same 3-option HiLL behavior in the workflow docs
• add explicit quick-start artifact persistence guidance so discovery.md, design.md, plan.md, implementation.md, project state.md, and refreshed .oat/state.md are committed at the right pause boundaries
• run oat sync --scope project, updating .oat/sync/manifest.json and creating the new provider skill symlinks for the oat-pjm-* skills under .claude/skills/ and .cursor/skills/

Verification

• pnpm run cli -- sync --scope project
• pnpm type-check
• pnpm lint
• pnpm format

Launch Plan

No runtime behavior or deploy steps. This changes skill instructions, docs, and synced provider views only.