feat: add Caveman Mode agent and instructions for low-token responses

[Philess]

Pull Request Checklist

• I have read and followed the CONTRIBUTING.md guidelines.
• I have read and followed the Guidance for submissions involving paid services.
• My contribution adds a new instruction, prompt, agent, skill, or workflow file in the correct directory.
• The file follows the required naming convention.
• The content is clearly structured and follows the example format.
• I have tested my instructions, prompt, agent, skill, or workflow with GitHub Copilot.
• I have run npm start and verified that README.md is up to date.
• I am targeting the staged branch for this pull request.

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Description

Added a custom agent and a custom instructions files to activate "Caveman" mode which highly reduce token consumption by simplifying to the max the response structure and sentences. (50 to 70%)
Usable as custom agent or with any other type of agent, plan mode and ask mode with the instructions file version

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Type of Contribution

• New instruction file.
• New prompt file.
• New agent file.
• New plugin.
• New skill file.
• New agentic workflow.
• Update to existing instruction, prompt, agent, plugin, skill, or workflow.
• Other (please specify):

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Additional Notes

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By submitting this pull request, I confirm that my contribution abides by the Code of Conduct and will be licensed under the MIT License.

[github-actions]

🔍 Skill Validator Results

⛔ Findings need attention

Scope	Checked
Skills	1
Agents	1
Total	2
Severity	Count
---	---:
❌ Errors	2
⚠️ Warnings	0
ℹ️ Advisories	0

Summary

Level	Finding
❌	[agent:Caveman Mode] Agent name 'Caveman Mode' does not match filename 'caveman-mode.agent.md' (expected 'Caveman Mode.agent.md').
❌	[agent:Caveman Mode] Agent name 'Caveman Mode' contains invalid characters — must be lowercase alphanumeric and hyphens only.

Full validator output

```text Found 1 agent(s) ❌ [agent:Caveman Mode] Agent name 'Caveman Mode' does not match filename 'caveman-mode.agent.md' (expected 'Caveman Mode.agent.md'). ❌ [agent:Caveman Mode] Agent name 'Caveman Mode' contains invalid characters — must be lowercase alphanumeric and hyphens only. Validated 1 agent(s)

{Ansi.Red}Agent spec conformance failures — fix the errors above.{Ansi.Reset}

</details>
> **Note:** The validator returned a non-zero exit code. Please review the findings above before merge.

[Copilot]

Pull request overview

Adds a “Caveman Mode” agent and companion custom instructions to encourage terse, low-token responses, and documents them in the repository indexes.

Changes:

• Added caveman-mode.instructions.md to provide low-token response directives via reusable instructions.
• Added caveman-mode.agent.md to offer the same behavior as a selectable custom agent.
• Updated the instructions and agents README indexes to include install links for the new files.

Show a summary per file

File	Description
instructions/caveman-mode.instructions.md	New instruction file defining terse/low-token response rules (with required front matter).
agents/caveman-mode.agent.md	New agent file defining “Caveman Mode” behavior (with required front matter).
docs/README.instructions.md	Adds the new instruction entry + install links to the instructions catalog.
docs/README.agents.md	Adds the new agent entry + install links to the agents catalog.

Copilot's findings

• Files reviewed: 4/4 changed files
• Comments generated: 0