Improve native-dependency-update skill instructions

[mattleibow]

Summary

Improves Phase 5 (Create PRs) of the native-dependency-update skill to prevent common mistakes.

Changes

• Add branch naming convention table for quick reference
• Add numbered sub-steps for SkiaSharp PR creation
• Add ⚠️ CRITICAL callout for submodule update requirement
• Add Phase 5 completion checklist to verify all steps before proceeding
• Use natural language instead of rigid bash scripts for flexibility

Why

During a libwebp update, I made these mistakes:

1. Used wrong branch naming (libwebp-1.6.0 instead of dev/update-libwebp)
2. Forgot to update the externals/skia submodule in the SkiaSharp PR
3. Didn't cross-link the PRs

The previous instructions had these issues buried in prose, making them easy to miss when moving quickly.

[github-actions]

Triage Summary

Labels will be applied to indicate the area of improvement (Documentation) and the relevant backend library (SkiaSharp) involved in the issue.

This issue is not a regression and does not involve compatibility, performance, or reliability issues.

Additional remarks:

• The issue centers on enhancing documentation to prevent mistakes during the native-dependency-update skill process, without direct ties to specific operating systems or performance concerns.

Detailed Summary and Actions

Summary of the triage:

• The issue focuses on improving documentation for the native-dependency-update skill, particularly to enhance instructions.
• Relevant improvements are noted for the SkiaSharp library in the context of PR creation.
• There are no operating system or performance labels applicable, indicating that the issue is not related to system compatibility or reliability.

Summary of the actions that will be performed:

Action	Item	Description
Apply Label	area/Docs	The issue involves improving documentation for the native-dependency-update skill.
Apply Label	backend/SkiaSharp	Improvements mentioned in relation to SkiaSharp which pertains specifically to PR creation.

This entire triage process was automated by AI and mistakes may have been made. Please let us know so we can continue to improve.