feat: add implementation completeness assurance rules

[shinpr]

Added new rule sections:

• Required procedure for impact analysis (3-stage process: Discovery → Understanding → Identification)
• Unused code deletion rule
• Existing code deletion decision flow

Key changes:

• Mandate not only Grep search but also reading all files and understanding context
• Immediate decision flow when unused code is detected (no deferral allowed)
• Clarify deletion criteria for existing code

Changed files:

• docs/rules-ja/ai-development-guide.md: Add Japanese rules
• docs/rules-ja/rules-index.yaml: Add sections and tags
• docs/rules-en/ai-development-guide.md: Add English rules
• docs/rules-en/rules-index.yaml: Add sections and tags
• package.json: v1.7.15 → v1.7.16
• package-lock.json: Version update

🤖 Generated with Claude Code