feat(claude): add PR size guidelines rule for business environments

[paveg]

Summary

• Add a Claude Code rule (~/.claude/rules/pr-size.md) that provides PR/commit size guidelines
• Only applied in business environments via chezmoi conditional ignore (.chezmoiignore)

Guidelines included

• PR size targets by language (Ruby/TS: 400 lines, Go/Java: 600 lines)
• Focus on "effective logic lines" (excluding generated code, test data)
• Commit granularity recommendations (100-200 lines per commit)
• Guidance for documenting larger PRs

Test plan

• Verify rule file is created with chezmoi apply in business environment
• Verify rule file is ignored in personal environment