docs(plugin-dev): document MessageDisplay streaming semantics

[iCodeCraft]

Summary

The bundled Hook Development skill currently omits MessageDisplay from its trigger description, event guidance, and quick-reference table, even though it is a supported hook event.

This PR documents MessageDisplay in the bundled plugin-development guidance:

• adds it to the skill trigger description and event table
• explains the streaming fields: message_id, index, final, and delta
• clarifies display-only behavior, per-message state, cleanup, and latency considerations
• links to the canonical MessageDisplay hook reference

Real-world motivation

This guidance was validated while building an opt-in MessageDisplay plugin that preserves Markdown-sensitive LaTeX escapes in terminal output:

• Plugin repository: https://github.com/iCodeCraft/claude-code-latex-terminal
• Release: https://github.com/iCodeCraft/claude-code-latex-terminal/releases/tag/v0.1.0
• Related user report: [Bug] LaTeX math corrupted by markdown escaping and not rendered in terminal output #80702

The plugin uses MessageDisplay as intended: it is display-only, preserves the transcript and model context, and maintains state per streamed message.

It is a workaround for LaTeX source corruption, not a replacement for native math rendering. Native rendering remains a separate feature request: #44479

Testing

• git diff --check

This is a documentation-only change that aligns the bundled skill with the existing MessageDisplay hook reference.