docs(skills): improve board connector guidance

[DR-Univer]

Summary

• recommend layered Board layout with practical node and corridor spacing;
• document Facade automatic routing selection and when explicit connector geometry is appropriate;
• add branch port separation, feedback-lane, narrow-corridor, and marker guidance;
• document terminal-direction and excessive-detour diagnostics.

Verification

• node_modules/.bin/oxfmt.cmd --check apps/cli/src/skills/runtime/board/SKILL.md
• node_modules/.bin/vitest.cmd run apps/cli/test/skills.test.ts apps/cli/test/authoring.test.ts (9 tests passed)

The repository-wide pnpm check was also attempted. In this Windows workspace it is currently blocked by unrelated existing full-repository formatting findings, a stale generated locale file, and platform-specific path and permission tests. No generated files, screenshots, scratch reports, dependency changes, or submodule gitlinks are included in this pull request.