refactor: shorten agent customization skill docs and clarify agent fields

[digitarald]

Based on team feedback, this PR refactors the agent customization skill documentation:

• Shortened all primitive docs - Reduced overall content by ~400 lines to keep prompts concise
• Removed prompt variables - Simplified by removing ${VAR} variable syntax examples that were adding confusion
• Clarified agent fields - Improved explanations for agent configuration properties like name, description, instructions, etc.

Affected files

• SKILL.md - Minor tweaks
• primitives/agents.md - Streamlined agent configuration docs
• primitives/instructions.md - Condensed instruction examples
• primitives/prompts.md - Simplified prompt documentation
• primitives/skills.md - Reduced skill configuration content
• primitives/workspace-instructions.md - Shortened workspace instruction docs

[Copilot]

Pull request overview

This PR refactors the agent customization skill documentation to improve clarity and conciseness by removing approximately 400 lines of content. The changes focus on streamlining documentation, removing complex variable syntax examples, and clarifying agent configuration field explanations.

Changes:

• Shortened all primitive documentation files by condensing verbose explanations into focused, actionable guidance
• Removed prompt variable syntax examples (${VAR}) that were adding unnecessary complexity
• Clarified agent configuration properties with improved explanations of fields like description, tools, infer, etc.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
workspace-instructions.md	Condensed file type documentation, simplified template sections, removed verbose creation process steps
skills.md	Streamlined SKILL.md format documentation, removed lengthy creation process and domain examples, simplified asset organization
prompts.md	Removed variable syntax documentation, condensed frontmatter examples, simplified templates and invocation instructions
instructions.md	Simplified discovery modes table, condensed template examples, removed verbose creation process steps
agents.md	Clarified infer field values with explicit table, updated tool alias names (shell→execute, custom-agent→agent), streamlined template and examples
SKILL.md	Minor description update to make trigger phrases more focused and scannable