Add gitmoji skill and gitmoji-setup agent (#2355)

* Add gitmoji skill and gitmoji-setup agent

Adds two complementary artifacts for the gitmoji commit convention
(https://gitmoji.dev):

- skills/gitmoji: generates gitmoji commit messages from a diff, staged
  changes, or a change description. Message-only by design (never runs
  git commands), with disambiguation rules and a full reference table of
  the 75 official gitmojis generated from the official gitmojis.json.
- agents/gitmoji-setup: sets up gitmoji tooling in a repository. Audits
  the existing hook manager and commit convention, then installs either
  a non-interactive prepare-commit-msg prefill hook (default, works in
  GUI clients and CI), the gitmoji-cli interactive picker, or commitlint
  enforcement, without clobbering existing hooks.

Generated README indexes updated via npm start.

* Use local commitlint binary instead of npx in verify step

Addresses the package-exec-command finding from the PR risk scan: the
verification example now calls the locally installed
./node_modules/.bin/commitlint rather than npx, which could fetch and
execute a package on the fly.

* Potential fix for pull request finding

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

* Address Copilot review feedback

- Quote the agent description in single quotes per AGENTS.md convention
- Resolve the effective hooks directory via git rev-parse --git-path
  hooks for both audit and installation, instead of hard-coding
  .git/hooks (core.hooksPath, linked worktrees)
- Correct the prefill-hook compatibility claim: it prefills only when
  the message editor opens and silently no-ops for -m/-F, GUI message
  boxes, and CI
- Match the official gitmoji set explicitly when detecting an existing
  emoji, instead of treating any non-ASCII start as one
- Drop .txt from the docs heuristic (it shadowed requirements.txt) and
  remove the dependency-manifest fallback entirely: filenames cannot
  distinguish upgrade/add/remove/pin/downgrade
- Restrict gitmoji -i to repos whose effective hooks dir is .git/hooks;
  wire the picker through the hook manager otherwise
- Merge gitmoji into an existing commitlint config instead of
  overwriting commitlint.config.mjs
- Fix the verification sequence: clean starting state, non-colliding
  scratch file, abort by clearing the editor, explicit unstage/remove/
  switch-back/branch-delete cleanup
- Skill: ask the user for commit history instead of running git log,
  honoring the message-only contract

* Address second round of Copilot review feedback

- Pair the prefill hook with a commit-msg guard: prefilling an empty
  COMMIT_EDITMSG defeats git abort-on-empty-message, so an untouched
  prefill would create a commit named only with the emoji. The guard
  rejects messages that contain nothing but the prefilled gitmoji.
- Extract the gitmoji alternation into a GITMOJI_RE variable shared by
  both hooks.
- Document the commitlint-config-gitmoji format mismatch: it enforces
  the hybrid <gitmoji> type(scope?): subject format and rejects the
  plain gitmoji format produced by Options A/B and the gitmoji skill.
  Option C now asks the team to choose a format first, and the
  verification example uses a valid hybrid message.

---------

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

skills/gitmoji/references/gitmoji-reference.md

@@ -0,0 +1,83 @@
+# Gitmoji Reference
+
+The complete official gitmoji list from [gitmoji.dev](https://gitmoji.dev/), in the order shown on the site. Each entry maps an emoji (and its `:shortcode:`) to the intent of the change it represents.
+
+| Emoji | Shortcode | Use for |
+|-------|-----------|---------|
+| 🎨 | `:art:` | Improve structure / format of the code. |
+| ⚡️ | `:zap:` | Improve performance. |
+| 🔥 | `:fire:` | Remove code or files. |
+| 🐛 | `:bug:` | Fix a bug. |
+| 🚑️ | `:ambulance:` | Critical hotfix. |
+| ✨ | `:sparkles:` | Introduce new features. |
+| 📝 | `:memo:` | Add or update documentation. |
+| 🚀 | `:rocket:` | Deploy stuff. |
+| 💄 | `:lipstick:` | Add or update the UI and style files. |
+| 🎉 | `:tada:` | Begin a project. |
+| ✅ | `:white_check_mark:` | Add, update, or pass tests. |
+| 🔒️ | `:lock:` | Fix security or privacy issues. |
+| 🔐 | `:closed_lock_with_key:` | Add or update secrets. |
+| 🔖 | `:bookmark:` | Release / Version tags. |
+| 🚨 | `:rotating_light:` | Fix compiler / linter warnings. |
+| 🚧 | `:construction:` | Work in progress. |
+| 💚 | `:green_heart:` | Fix CI Build. |
+| ⬇️ | `:arrow_down:` | Downgrade dependencies. |
+| ⬆️ | `:arrow_up:` | Upgrade dependencies. |
+| 📌 | `:pushpin:` | Pin dependencies to specific versions. |
+| 👷 | `:construction_worker:` | Add or update CI build system. |
+| 📈 | `:chart_with_upwards_trend:` | Add or update analytics or track code. |
+| ♻️ | `:recycle:` | Refactor code. |
+| ➕ | `:heavy_plus_sign:` | Add a dependency. |
+| ➖ | `:heavy_minus_sign:` | Remove a dependency. |
+| 🔧 | `:wrench:` | Add or update configuration files. |
+| 🔨 | `:hammer:` | Add or update development scripts. |
+| 🌐 | `:globe_with_meridians:` | Internationalization and localization. |
+| ✏️ | `:pencil2:` | Fix typos. |
+| 💩 | `:poop:` | Write bad code that needs to be improved. |
+| ⏪️ | `:rewind:` | Revert changes. |
+| 🔀 | `:twisted_rightwards_arrows:` | Merge branches. |
+| 📦️ | `:package:` | Add or update compiled files or packages. |
+| 👽️ | `:alien:` | Update code due to external API changes. |
+| 🚚 | `:truck:` | Move or rename resources (e.g.: files, paths, routes). |
+| 📄 | `:page_facing_up:` | Add or update license. |
+| 💥 | `:boom:` | Introduce breaking changes. |
+| 🍱 | `:bento:` | Add or update assets. |
+| ♿️ | `:wheelchair:` | Improve accessibility. |
+| 💡 | `:bulb:` | Add or update comments in source code. |
+| 🍻 | `:beers:` | Write code drunkenly. |
+| 💬 | `:speech_balloon:` | Add or update text and literals. |
+| 🗃️ | `:card_file_box:` | Perform database related changes. |
+| 🔊 | `:loud_sound:` | Add or update logs. |
+| 🔇 | `:mute:` | Remove logs. |
+| 👥 | `:busts_in_silhouette:` | Add or update contributor(s). |
+| 🚸 | `:children_crossing:` | Improve user experience / usability. |
+| 🏗️ | `:building_construction:` | Make architectural changes. |
+| 📱 | `:iphone:` | Work on responsive design. |
+| 🤡 | `:clown_face:` | Mock things. |
+| 🥚 | `:egg:` | Add or update an easter egg. |
+| 🙈 | `:see_no_evil:` | Add or update a .gitignore file. |
+| 📸 | `:camera_flash:` | Add or update snapshots. |
+| ⚗️ | `:alembic:` | Perform experiments. |
+| 🔍️ | `:mag:` | Improve SEO. |
+| 🏷️ | `:label:` | Add or update types. |
+| 🌱 | `:seedling:` | Add or update seed files. |
+| 🚩 | `:triangular_flag_on_post:` | Add, update, or remove feature flags. |
+| 🥅 | `:goal_net:` | Catch errors. |
+| 💫 | `:dizzy:` | Add or update animations and transitions. |
+| 🗑️ | `:wastebasket:` | Deprecate code that needs to be cleaned up. |
+| 🛂 | `:passport_control:` | Work on code related to authorization, roles and permissions. |
+| 🩹 | `:adhesive_bandage:` | Simple fix for a non-critical issue. |
+| 🧐 | `:monocle_face:` | Data exploration/inspection. |
+| ⚰️ | `:coffin:` | Remove dead code. |
+| 🧪 | `:test_tube:` | Add a failing test. |
+| 👔 | `:necktie:` | Add or update business logic. |
+| 🩺 | `:stethoscope:` | Add or update healthcheck. |
+| 🧱 | `:bricks:` | Infrastructure related changes. |
+| 🧑‍💻 | `:technologist:` | Improve developer experience. |
+| 💸 | `:money_with_wings:` | Add sponsorships or money related infrastructure. |
+| 🧵 | `:thread:` | Add or update code related to multithreading or concurrency. |
+| 🦺 | `:safety_vest:` | Add or update code related to validation. |
+| ✈️ | `:airplane:` | Improve offline support. |
+| 🦖 | `:t-rex:` | Code that adds backwards compatibility. |
+
+> Source: [gitmojis.json](https://github.com/carloscuesta/gitmoji/blob/master/packages/gitmojis/src/gitmojis.json) — 75 gitmojis.