Migrate extension packaging to HVE Core component model

[coatsy]

Summary

Restructure this repository from a fork of microsoft/skills-for-copilot-studio into a standalone component that contributes to the HVE Core extension (ise-hve-essentials.hve-core), rather than being published as an independent extension under the coatsy publisher.

Sub-tasks

• Phase 1: Disentangle from upstream fork (Phase 1: Disentangle from upstream fork #34) — remove fork relationship, replace merge-based sync with build-time content fetch. Extension continues publishing as coatsy.copilot-studio-skills.
• Phase 2: Migrate to HVE Core component (Phase 2: Migrate to HVE Core extension component #35) — restructure to HVE Core conventions, move to ise-hve-essentials publisher, eliminate build-time frontmatter transformation.

Background

Current architecture

• This repo is a fork of microsoft/skills-for-copilot-studio.
• The extension is published as coatsy.copilot-studio-skills with a companion extension pack coatsy.copilot-studio-development-bundle.
• Versioning is synchronized with upstream releases via upstream-version.json, enforced by validate-versions.yml and check-upstream-release.yml.
• The build pipeline (extension/test-local.sh) stages artifacts from the fork, transforms Claude Code-specific frontmatter to VS Code format, discovers agents/skills dynamically, generates package.json, and packages a .vsix.
• Publishing is triggered by GitHub Releases and uses a VSCE_PAT secret to push to the VS Code Marketplace under the coatsy publisher.

Target architecture (HVE Core component)

• HVE Core (ise-hve-essentials.hve-core, v3.3.101) is a pre-built VS Code extension published by ise-hve-essentials (Microsoft ISE).
• It uses contributes.chatAgents, contributes.chatSkills, contributes.chatPrompts, and contributes.chatInstructions to register its 18 agents, 15+ prompts, 7 instruction files, and 1 skill.
• Content lives under .github/ (agents, skills, instructions, prompts) and is packaged directly — no build-time transformation step.

Acceptance criteria

• Repository is no longer a GitHub fork of microsoft/skills-for-copilot-studio
• Upstream content is fetched at build time (not via fork merge)
• Extension layout matches HVE Core conventions
• Build and publish pipelines produce a valid .vsix under the target publisher
• All existing agents (4) and skills (33) are registered and functional
• CI validates the built extension (agent/skill counts, no stale references)
• Documentation updated to reflect new architecture