docs: clarify official documentation discrepancies in agent-development skill (#124)

## Summary

Adds clarification notes to the agent-development skill explaining
documentation discrepancies between this skill and official Claude Code
documentation.

## Problem

Fixes #123

Users following the agent-development skill may be confused when
comparing it to official Claude Code documentation because:
1. The `color` field is documented here but not in the [official
sub-agents docs](https://docs.claude.com/en/docs/claude-code/sub-agents)
2. The
[plugins-reference.md](https://docs.claude.com/en/docs/claude-code/plugins-reference)
shows an older agent format using `capabilities` instead of `tools`

## Solution

Added clarification notes in two locations:
1. **Overview section** - Comprehensive note explaining both
discrepancies and linking to
[anthropics/claude-code#8501](anthropics/claude-code#8501)
for upstream tracking
2. **`color` field section** - Brief note pointing back to the overview
for details

### Alternatives Considered

- Adding a dedicated "Documentation Notes" section: Rejected as it would
add too much visual weight for a temporary discrepancy
- Only documenting at the `color` field: Rejected as users need context
early in the document

## Changes

- `plugins/plugin-dev/skills/agent-development/SKILL.md`: Added
clarification notes about official documentation discrepancies

## Testing

- [x] Linting passes (`markdownlint`)
- [x] Links to upstream issue and docs are valid

---
🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude <noreply@anthropic.com>

Author: sjnims

plugins/plugin-dev/skills/agent-development/SKILL.md

@@ -17,6 +17,8 @@ Agents are autonomous subprocesses that handle complex, multi-step tasks indepen
 - Model and color customization
 
 > **Important - Field Name Difference:** Agents use `tools` to restrict tool access. Skills use `allowed-tools` for the same purpose. Don't confuse these when switching between component types.
+>
+> **Note on Official Documentation:** The `color` field documented in this skill is supported by Claude Code and is generated by the built-in `/agents` command, but it is not yet reflected in the [official sub-agents documentation](https://docs.claude.com/en/docs/claude-code/sub-agents). See [anthropics/claude-code#8501](https://github.com/anthropics/claude-code/issues/8501) for tracking. The [plugins-reference.md](https://docs.claude.com/en/docs/claude-code/plugins-reference) may show an older agent format using a `capabilities` field; for Claude Code plugins, prefer the structure documented in this skill which uses `tools` for tool restrictions.
 
 ## Quick Start
 
@@ -206,6 +208,8 @@ Which model the agent should use.
 
 Visual identifier for agent in UI.
 
+> **Note:** This field is supported by Claude Code but not yet in official documentation. See the [Overview note](#overview) for details.
+
 **Options:** `blue`, `cyan`, `green`, `yellow`, `magenta`, `red`
 
 **Guidelines:**