New skill: issue-fields-migration (#990)

* Add issue-fields-migration skill

Standalone skill to bulk-copy field values from Project V2 fields to
org-level issue fields. Includes 5-phase workflow (discovery, option
mapping, data scan, preview/dry-run, execution) with API references
for issue fields REST API and Projects V2 API.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Expand issue-fields-migration skill to support label migration

Add support for migrating repo-based labels to org-level issue fields,
in addition to the existing project field migration flow.

Changes:
- Add Step 0 routing: ask user if migrating labels or project fields
- Add Label Migration Flow (Phases L1-L5) with conflict detection,
  bulk mapping, and optional label removal
- Add labels API to Available Tools table
- Create references/labels-api.md
- Add 3 label migration examples (single, bulk, cross-repo)
- Expand Important Notes with label-specific guidance
- Rename existing phases to P1-P6 under Project Field Migration Flow
- Include P1 fixes from prior work (proxy field filtering, batch
  option mapping, preflight permission checks, pagination fixes)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* fix: payload format, field_id type + 10 UX/scale improvements

Bug fixes:
- Wrap write endpoint payload in {"issue_field_values": [...]} (was bare array)
- Use integer field_id, not string (both Phase L5 and P6)

UX improvements:
- Label filtering guidance for repos with 50+ labels
- Smarter auto-suggest with 4 pattern tiers (exact, prefix-number, strip-separators, substring)
- Handle zero-issue labels gracefully (stop and suggest alternatives)
- Add time estimates to migration previews
- Document read response shape (.single_select_option.name vs .value)

Scale & reliability:
- Script generation guidance for 100+ issue migrations
- Idempotent/resumable migration note
- Warn about --limit 1000 silent truncation
- Warn about macOS bash 3.x (no declare -A)
- PR filtering guidance (type field)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Update README.skills.md with build

Regenerated skills index to reflect label migration support and
updated references for issue-fields-migration skill.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Address PR review comments: fix MCP conventions, step numbering, pagination, phase refs

- Align MCP tool calls with repo conventions (method: instead of action:,
  owner: instead of project_owner:) in SKILL.md and projects-api.md
- Fix step numbering in Phase P2 (duplicate step 5 → renumber to 6)
- Update example phase references to use P1-P6/P1-P5 labels
- Add pageInfo pagination to GraphQL fields and fieldValues queries
- Fix MCP tool name in labels-api.md to mcp__github__list_issues

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

---------

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

docs/README.skills.md

@@ -135,6 +135,7 @@ See [CONTRIBUTING.md](../CONTRIBUTING.md#adding-skills) for guidelines on how to
 | [go-mcp-server-generator](../skills/go-mcp-server-generator/SKILL.md) | Generate a complete Go MCP server project with proper structure, dependencies, and implementation using the official github.com/modelcontextprotocol/go-sdk. | None |
 | [image-manipulation-image-magick](../skills/image-manipulation-image-magick/SKILL.md) | Process and manipulate images using ImageMagick. Supports resizing, format conversion, batch processing, and retrieving image metadata. Use when working with images, creating thumbnails, resizing wallpapers, or performing batch image operations. | None |
 | [import-infrastructure-as-code](../skills/import-infrastructure-as-code/SKILL.md) | Import existing Azure resources into Terraform using Azure CLI discovery and Azure Verified Modules (AVM). Use when asked to reverse-engineer live Azure infrastructure, generate Infrastructure as Code from existing subscriptions/resource groups/resource IDs, map dependencies, derive exact import addresses from downloaded module source, prevent configuration drift, and produce AVM-based Terraform files ready for validation and planning across any Azure resource type. | None |
+| [issue-fields-migration](../skills/issue-fields-migration/SKILL.md) | Migrate field values from GitHub Project V2 fields or repo labels to org-level issue fields. Use this skill when users need to bulk-copy metadata (priority, status, dates, text, numbers) from project fields or labels to issue fields, or when they ask about migrating, transferring, or copying project field data or labels to issue fields. | `references/issue-fields-api.md`<br />`references/labels-api.md`<br />`references/projects-api.md` |
 | [java-add-graalvm-native-image-support](../skills/java-add-graalvm-native-image-support/SKILL.md) | GraalVM Native Image expert that adds native image support to Java applications, builds the project, analyzes build errors, applies fixes, and iterates until successful compilation using Oracle best practices. | None |
 | [java-docs](../skills/java-docs/SKILL.md) | Ensure that Java types are documented with Javadoc comments and follow best practices for documentation. | None |
 | [java-junit](../skills/java-junit/SKILL.md) | Get best practices for JUnit 5 unit testing, including data-driven tests | None |