Add changesets skill and update PR creation instructions

.github/copilot-instructions.md

@@ -154,4 +154,8 @@ When working on UI components, always use the `primer-storybook` MCP tools to ac
 
 ## Pull Request Creation
 
-When creating a pull request, you MUST use the template in `.github/pull_request_template.md` to structure the PR description. Read the template file, fill in all sections appropriately, and include it in the PR body.
+When creating a pull request, you MUST:
+
+1. Use the template in `.github/pull_request_template.md` to structure the PR description. Read the template file, fill in all sections appropriately, and include it in the PR body.
+2. Include a changeset file in the PR if the change affects the published package (bug fix, new feature, breaking change, etc.). Create a `.changeset/<descriptive-name>.md` file with the appropriate semver bump type. Reference the `changesets` skill (`.github/skills/changesets/SKILL.md`) for detailed guidance on file format, choosing the correct bump type, and when a changeset can be skipped.
+3. If no changeset is needed (docs-only, test-only, CI/infra changes), add the `skip changeset` label to the pull request to bypass the CI changeset check.

.github/skills/changesets/SKILL.md

@@ -0,0 +1,117 @@
+---
+name: changesets
+description: 'Use when: adding changesets to pull requests, determining semver bump types, versioning packages, or preparing releases. Covers changeset file format, semver guidance, when changesets are required, and the release pipeline.'
+---
+
+# Changesets in Primer React
+
+This repository uses [Changesets](https://github.com/changesets/changesets) to manage versioning and changelogs. Every pull request that changes the public API or runtime behavior of a package must include a changeset file.
+
+## What is a changeset?
+
+A changeset is a markdown file in the `.changeset/` directory that describes:
+
+1. **Which package** is affected (e.g., `@primer/react`)
+2. **What semver bump** to apply (`patch`, `minor`, or `major`)
+3. **A human-readable description** of the change (used in the changelog)
+
+## File format
+
+Changeset files live in `.changeset/` and have a random name with a `.md` extension. The file uses YAML frontmatter to specify the package and bump type, followed by a description:
+
+```markdown
+---
+'@primer/react': patch
+---
+
+ActionMenu: Fix focus management when menu is closed with Escape key
+```
+
+The description should be concise and follow this pattern:
+
+- Start with the component or module name followed by a colon
+- Describe WHAT changed and WHY
+- Write from the consumer's perspective
+
+## How to create a changeset
+
+### Option 1: Interactive CLI
+
+Run `npx changeset` and follow the prompts to select the package, bump type, and enter a description.
+
+### Option 2: Manually create a file
+
+Create a new file in `.changeset/` with a unique name (e.g., `.changeset/my-change-description.md`):
+
+```markdown
+---
+'@primer/react': minor
+---
+
+Avatar: Add `square` variant for non-user avatars
+```
+
+Use lowercase kebab-case for the filename. The name is arbitrary but should be descriptive.
+
+## Choosing the correct semver bump
+
+Use this quick reference to determine the bump type. For the full decision table with detailed examples, see `contributor-docs/versioning.md`.
+
+### `patch` — Bug fixes and internal corrections
+
+- Fix a bug in component behavior
+- Fix a styling issue
+- Fix a TypeScript type that was incorrect
+- Internal refactor that does not change the public API
+
+### `minor` — New features and non-breaking additions
+
+- Add a new component
+- Add a new prop to an existing component
+- Broaden the type of an existing prop (e.g., `string` → `string | number`)
+- Deprecate a component or prop
+- Add a new export
+- Add a `data-component` attribute
+- Add a dependency
+
+### `major` — Breaking changes
+
+- Remove a component
+- Remove a prop
+- Narrow the type of a prop (e.g., `string` → `'a' | 'b'`)
+- Change the element that props are spread onto
+- Broaden the element type in an event handler
+- Remove or rename a `data-component` attribute
+- Bump a dependency to a new major version
+
+## When a changeset is NOT needed
+
+Skip the changeset for changes that do not affect the published package:
+
+- Documentation-only changes (markdown files, docs site content)
+- Test-only changes (adding or updating tests)
+- CI/infrastructure changes (GitHub Actions, scripts, config files)
+- Storybook stories that don't change component source
+- Dev dependency updates
+- Changes to `examples/` or `e2e/` directories
+
+When a changeset is not needed, add the `skip changeset` label to the pull request. This bypasses the CI check that requires a changeset to be present.
+
+## Multiple changesets in one PR
+
+If a PR introduces multiple distinct changes, add a **separate changeset file for each**. For example, if you fix a bug in `Button` and add a new prop to `ActionMenu`, create two changeset files — one `patch` for the fix and one `minor` for the new prop.
+
+## Release pipeline
+
+Understanding the release pipeline helps explain why changesets are required:
+
+1. **On PR creation**: `changeset-bot` comments on the PR indicating whether valid changesets are present. If your change requires a changeset and none is found, the bot will flag it.
+2. **On merge to `main`**: The `changesets/action` GitHub Action automatically creates or updates a "Version Packages" release PR that bumps version numbers, updates `CHANGELOG.md`, and shows release notes.
+3. **On merging the release PR**: The action publishes the new version to npm and creates a GitHub Release.
+
+## Common files
+
+- `.changeset/*.md` — Changeset files (one per change)
+- `.changeset/config.json` — Changesets configuration
+- `contributor-docs/versioning.md` — Detailed semver bump guidance
+- `contributor-docs/CONTRIBUTING.md` — Contributing guidelines including changeset instructions