Add @probo/skills multi-agent compliance package

Ship compliance skills and agent plugin wiring for Claude Code,
Codex, OpenCode, and Cursor via Probo MCP (OAuth 2.0). Includes
access-review and missing-signatures workflows, repo-root Git
marketplaces, validation, and npm release CI.

Signed-off-by: Cursor Agent <cursoragent@cursor.com>

Co-authored-by: Bryan FRIMIN <bryan@frimin.fr>

packages/skills/CHANGELOG.md

@@ -0,0 +1,29 @@
+# Changelog
+
+All notable changes to the `@probo/skills` package will be documented in
+this file.
+
+## Unreleased
+
+### Added
+
+- `@probo/skills` npm package with multi-agent manifests (`.claude-plugin/`,
+  `.codex-plugin/`, `.agents/`) and Probo MCP wiring via `.mcp.json`
+  (`PROBO_BASE_URL`, OAuth 2.0 sign-in)
+- Skills: `open-source-compliance`, `access-review`, `missing-signatures`
+- Commands: `access-review`, `missing-signatures` (Claude Code slash commands
+  delegating to shared skills)
+- Portable relative `references/` paths in skill bodies (no
+  `${CLAUDE_PLUGIN_ROOT}`)
+- Resumable session notes for `access-review` and `missing-signatures`
+- Repo-root marketplace catalogs for Git installs (`getprobo/probo`):
+  `.claude-plugin/marketplace.json` (Claude Code) and
+  `.agents/plugins/marketplace.json` (Codex)
+- Package-local marketplace catalogs under `packages/skills/`
+- `COMPATIBILITY.md`, validation script, and release workflow
+  (`release-npm-skills.yaml`, tag `@probo/skills/v*`)
+
+### Changed
+
+- Package published as `@probo/skills` in `packages/skills/` (multi-agent
+  scope, not Claude-specific)