fix: add complete frontmatter to onboard.md

[xiaolai]

Automated audit: This PR was generated by NLPM, a natural language programming linter, running via claude-code-action. Please evaluate the diff on its merits.

Bug

.claude/commands/onboard.md has no frontmatter at all. The other five commands in this repo all have a proper --- frontmatter block; onboard.md starts directly with # Onboard.

This causes three concrete problems:

1. Missing name — the /onboard command cannot be registered or invoked by name
2. Missing description — the command has no discoverable description for the UI or skill-routing hooks
3. Missing allowed-tools — Claude has no declared tool boundary, so it may use arbitrary tools when running this command

Fix

Added a standard frontmatter block consistent with the repo's other commands:

+---
+name: onboard
+description: Onboard Claude to a new task by exploring the codebase and preparing a task brief
+allowed-tools: Read, Glob, Grep, Write, Bash(find:*)
+---
+
 # Onboard

The allowed-tools list covers exactly what the command body needs:

• Read, Glob, Grep — codebase exploration
• Write — creating the .claude/tasks/[TASK_ID]/onboarding.md file
• Bash(find:*) — optional filesystem discovery

No behavior is changed in the command body.