docs: clarify version field in agent-development skill

[sjnims]

Summary

The agent-development SKILL.md frontmatter includes a version field, but this field is not documented in the Frontmatter Fields section for agents.

Current State

SKILL.md frontmatter:

---
name: agent-development
description: This skill should be used when...
version: 0.1.0  # <-- This field exists but isn't documented for agents
---

The documented agent frontmatter fields are:

• name (required)
• description (required)
• model (required)
• color (required)
• tools (optional)

No mention of version.

Questions to Resolve

1. Is version a valid field for agent frontmatter?
2. If yes, should it be documented in the Frontmatter Fields section?
3. If no, should it be removed from the SKILL.md frontmatter (it may be a skill field, not agent field)?

Context

The version field appears to be for the skill itself (SKILL.md), not for agents. The skill documents how to create agents, and agent examples don't show a version field.

Proposed Resolution

Option A: Remove version from SKILL.md frontmatter if it's not a valid skill field

Option B: Keep version and add a note that this is for the skill metadata, separate from agent frontmatter

Option C: If version IS valid for agents, document it in the Frontmatter Fields section

Acceptance Criteria

• Clarity on whether version is valid for skills/agents
• Consistent documentation of all valid fields
• No undocumented fields in examples

[sjnims]

PR submitted: #16