feat: bring Copilot Studio development agents and skills into HVE Core

Nobody has claimed this yet.

### Issue Description

## Summary

Propose folding the Copilot Studio development agents and skills (currently shipped as the standalone `coatsy.copilot-studio-skills` VS Code extension) into HVE Core as a content collection, so makers and pro-users get first-class Copilot Studio authoring/management/testing/troubleshooting support inside the same auto-updating extension as the rest of HVE Core.

## Background

- The Copilot Studio CAT team published a set of [agents and skills for Copilot Studio development](https://github.com/microsoft/skills-for-copilot-studio), targeting Claude and the GitHub Copilot CLI.
- I built a reformatting/publishing layer that makes them work in VS Code GitHub Copilot Chat, shipped as [`coatsy.copilot-studio-skills`](https://marketplace.visualstudio.com/items?itemName=coatsy.copilot-studio-skills) (four agents — authoring, managing, testing, troubleshooting — plus ~24 skills).
- The CAT team have indicated they'd rather not take the VS Code packaging into their own repo. With agreement from @WilliamBerryiii, the plan is to bring it into HVE Core.
- Demand signal: the standalone extension has reached over 900 downloads with no publicity.

## Why HVE Core

- Extends HVE Core's reach into low-code/maker and pro-user workflows alongside its existing pro-code agents, complementing the planned project-planning, early-SDLC, and incident-management capabilities.
- The authoring skills address concrete failure modes (e.g. avoiding hallucination of the `kind:` property in generated Copilot Studio YAML), so they raise quality, not just coverage.
- HVE Core's auto-updating extension delivery model is exactly the distribution mechanism this content needs (it's what inspired the original extension).

## Proposed approach

Adopt HVE Core conventions:

- `.github/agents/copilot-studio/` — `.agent.md` files
- `.github/skills/copilot-studio/` — skill directories with `SKILL.md`
- `.github/instructions/` — any instruction files, if applicable
- Native VS Code chat frontmatter (no Claude Code-specific fields)

## Integration model

Recommending **Option A**: contribute the content directly into the `ise-hve-essentials.hve-core` extension (agents/skills live in the HVE Core repo) in a copilot-studio-skills extension.

Alternative considered — Option B: keep it a separate extension but publish under the `ise-hve-essentials` publisher, following HVE Core conventions.

Seeking HVE Core maintainers' view on the preferred integration model and any contribution requirements.

## Migration plan

The work is staged in the source repo (`coatsy/skills-for-copilot-studio`) in two phases:

- **Phase 1 — disentangle from the upstream fork.** Remove the fork relationship to `microsoft/skills-for-copilot-studio` and replace merge-based sync with a build-time content fetch, so updates from the CAT team are pulled rather than merged. The extension continues publishing as `coatsy.copilot-studio-skills` during this phase.
- **Phase 2 — migrate to the HVE Core component model.** Restructure the repo to HVE Core conventions (`.github/agents`, `.github/skills`, native VS Code chat frontmatter), eliminate the build-time Claude Code frontmatter transformation, and move publishing to the `ise-hve-essentials` publisher (Option A: contributed directly into the HVE Core repo).

## Upstream sync

The content originates from [`microsoft/skills-for-copilot-studio`](https://github.com/microsoft/skills-for-copilot-studio). This is already automated: releases in the upstream repo are monitored, and an automatic PR is raised with the updated agents and skills. Moving into HVE Core means retargeting that existing automation (build-time content fetch / auto-PR) at the HVE Core repo, so the content keeps tracking CAT team updates without a fork merge.

### Additional Context

_No response_

Review HVE Core's existing component conventions alongside the proposed .github/agents/copilot-studio/, .github/skills/copilot-studio/, and .github/instructions/ paths. Inspect the automation in coatsy/skills-for-copilot-studio and the upstream microsoft/skills-for-copilot-studio source before confirming the integration model. Done means the Copilot Studio agents and skills are incorporated with native VS Code frontmatter and automated upstream updates.

Written by the indexing model from the issue text.