docs(plugin-dev): improve skill documentation quality and reduce context size

[sjnims]

Summary

This PR improves the plugin-dev skills with a focus on leaner documentation and better consistency:

• Reduced context size: Cut skill-development SKILL.md from 3,196→1,298 words (~60% reduction) and command-development SKILL.md from 2,426→1,962 words (~20% reduction) by moving detailed content to references
• Added missing references: Created references/skill-creation-workflow.md and references/plugin-integration.md for content moved from SKILL.md files
• Improved consistency: Fixed description wording to use "asks to" instead of "wants to" across skills
• Better citations: Made plugin-structure reference citations explicit with direct file paths
• Removed bash execution triggers: Cleaned up command-development examples that could accidentally trigger bash execution
• Consolidated hook format docs: Unified the plugin hooks.json format explanation in hook-development

These changes follow the progressive disclosure principle - keeping SKILL.md files lean while making detailed information available in reference files.

Test plan

• [ ] Verify plugin-dev skills load correctly with cc --plugin-dir plugins/plugin-dev
• [ ] Test skill triggering works with phrases like "create a skill", "add a command"
• [ ] Confirm reference files are accessible and well-structured

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