Relocate PR lifecycle to canonical states and add ai-ready-kit PR contract

[SoundBlaster]

Motivation

• Make the PR lifecycle the single authoritative execution signal by moving the Draft/Ready/Merged semantics into the core states section so tooling and contributors have one canonical source of truth.
• Clarify repository-level PR conventions by providing an exact ai-ready-kit contract for title format, required labels, and the Markdown check to reduce ambiguity and ensure automated validation.

Description

• Moved the Draft PR lifecycle definition into the canonical operational states in kit/docs/agent-ready/en/RFC_AGENT_READY_WORKPLAN_ISSUES_PROTOCOL_v0.1.en.md and removed the duplicate wording.
• Added an exact ai-ready-kit repository contract to kit/docs/agent-ready/en/RFC_AGENT_READY_QUALITY_CONTRACT_v0.1.en.md that requires PR title format [<TASK_ID>] <short summary>, enumerates required labels, and documents the required Markdown check (make md-check).
• Resolved target-branch conflict by updating the files and committing the relocated section and contract changes to the branch.

Testing

• Docs-only changes; no automated tests were run.
• Changes were staged and committed locally (git commit) successfully and are ready for review as documentation updates.

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Codex Task