feat: add /generate-changelog slash command (#287)

Move changelog generation prompt from publish.yml into a reusable slash
command at .claude/commands/generate-changelog.md. Update workflow to
call the command with version parameters.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude <noreply@anthropic.com>

.claude/commands/generate-changelog.md

@@ -0,0 +1,19 @@
+---
+allowed-tools: Edit, Bash(git add:*), Bash(git commit:*)
+description: Generate changelog for a new release version
+---
+
+You are updating the changelog for the new release.
+
+Update CHANGELOG.md to add a new section for the new version at the top of the file, right after the '# Changelog' heading.
+
+Review the recent commits and merged pull requests since the last release to generate meaningful changelog content for the new version. Follow the existing format in CHANGELOG.md with sections like:
+- Breaking Changes (if any)
+- New Features
+- Bug Fixes
+- Documentation
+- Internal/Other changes
+
+Include only the sections that are relevant based on the actual changes. Write clear, user-focused descriptions.
+
+After updating CHANGELOG.md, commit the changes with the message "docs: update changelog for v{new_version}".

.github/workflows/publish.yml

@@ -133,21 +133,7 @@ jobs:
         continue-on-error: true
         uses: anthropics/claude-code-action@v1
         with:
-          prompt: |
-            You are updating the changelog for the new release v${{ env.VERSION }}.
-
-            Update CHANGELOG.md to add a new section for version ${{ env.VERSION }} at the top of the file, right after the '# Changelog' heading.
-
-            Review the recent commits and merged pull requests since the last release (${{ steps.previous_tag.outputs.previous_tag }}) to generate meaningful changelog content for v${{ env.VERSION }}. Follow the existing format in CHANGELOG.md with sections like:
-            - Breaking Changes (if any)
-            - New Features
-            - Bug Fixes
-            - Documentation
-            - Internal/Other changes
-
-            Include only the sections that are relevant based on the actual changes. Write clear, user-focused descriptions.
-
-            After updating CHANGELOG.md, commit the changes with the message "docs: update changelog for v${{ env.VERSION }}".
+          prompt: /generate-changelog new version: ${{ env.VERSION }}, old version: ${{ steps.previous_tag.outputs.previous_tag }}
           anthropic_api_key: ${{ secrets.ANTHROPIC_API_KEY }}
           github_token: ${{ secrets.GITHUB_TOKEN }}
           claude_args: |