feat: add github-issue-workflow skill

Add a new skill that guides users through the complete GitHub issue
workflow: issue selection, development, PR creation, code review,
and merge following ITK-dev conventions.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: yepzdk

skills/github-issue-workflow.md

@@ -0,0 +1,58 @@
+---
+name: github-issue-workflow
+description: Work through GitHub issues following the ITK-dev workflow. Use this skill when you need to pick an issue, develop a solution, create a PR, review code, and merge. Handles the complete development lifecycle from issue selection to merge.
+---
+
+# GitHub Issue Workflow
+
+You are working through GitHub issues following the ITK-dev workflow. Execute these steps:
+
+## PHASE 1: Issue Selection
+1. Run `gh issue list --state open --limit 20` to show open issues
+2. Ask the user which issue to work on (or let them specify one)
+3. Run `gh issue view <number>` to get full details
+4. Summarize the issue and confirm understanding with the user
+
+## PHASE 2: Development
+1. Switch to main branch and pull latest: `git checkout main && git pull`
+2. Create feature branch: `git checkout -b feature/issue-<number>-<short-description>`
+3. Plan the implementation (use EnterPlanMode for non-trivial tasks)
+4. Implement the solution following project guidelines in CLAUDE.md
+5. Update CHANGELOG.md with the changes
+6. Run `task ci` to verify all checks pass
+7. Fix any issues until CI passes
+
+## PHASE 3: Create PR
+1. Commit changes with descriptive message referencing the issue
+2. Push branch: `git push -u origin <branch-name>`
+3. Create PR with `gh pr create` following this format:
+   - Title: Brief description (Closes #<issue-number>)
+   - Body: ## Summary (bullet points), ## Test plan (checkboxes)
+
+## PHASE 4: UI Testing (if applicable)
+1. Ask user if this change has UI components that need testing
+2. If yes, use the dev-browser skill or browser-feedback tools to test
+3. Document any UI issues found and fix them
+
+## PHASE 5: Code Review
+1. Use the Task tool with subagent_type='pr-review-toolkit:code-reviewer' to review the changes
+2. Also run 'pr-review-toolkit:silent-failure-hunter' for error handling review
+3. Present review findings to user
+4. Fix any issues identified in review
+5. Push fixes and re-run CI if needed
+
+## PHASE 6: Merge
+1. Confirm with user that PR is ready to merge
+2. Run `gh pr merge --squash --delete-branch` to merge
+3. Switch back to main: `git checkout main && git pull`
+
+## PHASE 7: Next Issue
+1. Ask user if they want to continue with another issue
+2. If yes, return to Phase 1
+
+## Important Guidelines
+- Always follow CLAUDE.md guidelines
+- Never commit directly to main
+- Always run `task ci` before creating PR
+- All user-facing text in Danish, code/commits in English
+- Ask for clarification if requirements are unclear