feat: add Delegation Boundary and improve orchestration guide precision

[shinpr]

Summary

• Add "Delegation Boundary: What vs How" section to orchestration guide — defines what/where/constraints the orchestrator passes vs what specialists determine autonomously
• Scope granularity per agent type: executor agents receive task file paths (broader scope requires explicit user request); discovery/review agents receive directory scope with read-only access
• 4-tier decision precedence for conflict resolution (user instructions > design artifacts > repo state > specialist judgment)
• Convert "Prohibited Actions" to positive-form "Required Actions" — negative instructions cause LLMs to focus on the prohibited behavior instead of the desired behavior
• Restructure Structured Response Specifications from bullet list to Agent/Key Fields/Decision Logic table with quality-fixer blocked handling as a dedicated subsection
• Clean remaining negative-form instructions: "no modification" → "read-only access", remove "instead of guessing", replace vague "higher-precedence source" with explicit ordering
• All changes applied to both EN and JA versions; fix one missing operational line in JA

Test plan

• Verify EN orchestration guide renders correctly with new Delegation Boundary section
• Verify JA orchestration guide renders correctly with equivalent changes
• Confirm Structured Response table and quality-fixer subsection are scannable
• Check EN/JA symmetry — no missing sections or semantic drift

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