docs: add Agent Skills SKILL.md

Add a root-level SKILL.md that follows the Agent Skills specification and guides agents to Commitizen commands, configuration, versioning, changelog, CI, and exit-code references.

Refs: #1936

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

Author: bearomorphism

SKILL.md

@@ -0,0 +1,74 @@
+---
+name: commitizen
+description: Use this skill for tasks involving Conventional Commits, commit message validation, Commitizen configuration, semantic version bumps, changelog generation, or CI/release automation with the Commitizen CLI.
+license: MIT
+compatibility: Git repository with Python and Commitizen available as `cz` or runnable from source. Network access is optional and mainly relevant for CI or release integrations.
+metadata:
+  project: commitizen-tools/commitizen
+  docs: https://commitizen-tools.github.io/commitizen/
+  install: pip install commitizen | uv add commitizen
+---
+
+# Commitizen
+
+Commitizen is a CLI for enforcing Conventional Commits, automating version bumps, and generating changelogs.
+
+## Use this skill when
+
+- A task involves commit message authoring or validation.
+- A repository needs Commitizen initialization or configuration updates.
+- Work depends on version schemes, version providers, version files, tags, or changelog behavior.
+- CI/CD automation needs commit validation, automated version bumps, or release notes.
+
+## Core workflow
+
+1. Find the active configuration file in this order: `.cz.toml`, `cz.toml`, `.cz.json`, `cz.json`, `.cz.yaml`, `cz.yaml`, then `pyproject.toml` under `[tool.commitizen]`.
+2. Read the effective settings before acting, especially `name`, `version`, `version_provider`, `version_scheme`, `version_files`, `tag_format`, `update_changelog_on_bump`, `annotated_tag`, `bump_message`, `pre_bump_hooks`, and `post_bump_hooks`.
+3. Match the command to the task:
+   - `cz commit` for interactive commit authoring
+   - `cz check` for validating commit messages or git ranges
+   - `cz init` for bootstrapping configuration
+   - `cz bump` for calculating or applying release versions
+   - `cz changelog` for generating or updating `CHANGELOG.md`
+   - `cz ls` for listing available commit rules
+   - `cz version` for showing the current version
+4. Prefer read-only inspection first. Safe discovery commands include `cz version`, `cz ls`, `cz check`, `cz bump --get-next`, and `cz bump --dry-run`.
+5. Treat `cz bump` as stateful: it can update version files, create a bump commit, and create a git tag. Verify the version provider, version scheme, tag format, and changelog settings before running it for real.
+6. When automating in CI, check whether the workflow should ignore specific exit codes with `--no-raise` and whether `bump_message` should include skip-CI text.
+7. After making changes, validate the resulting configuration, commands, and automation against the repository's actual version scheme and provider.
+
+## Important domain details
+
+- Commitizen installs with `pip install commitizen` or `uv add commitizen`.
+- The default version scheme is PEP 440; `semver` and `semver2` are also supported.
+- Common version providers include `commitizen`, `pep621`, `poetry`, `cargo`, `npm`, `composer`, `uv`, and `scm`.
+- `cz changelog` generates Markdown changelogs.
+- `cz commit` supports `--dry-run` and `--write-message-to-file`.
+- `cz check` can validate a literal message, a commit-msg file, or a git revision range.
+
+## Suggested references
+
+- Command docs:
+  - `docs/commands/commit.md`
+  - `docs/commands/bump.md`
+  - `docs/commands/changelog.md`
+  - `docs/commands/check.md`
+  - `docs/commands/init.md`
+- Config docs:
+  - `docs/config/configuration_file.md`
+  - `docs/config/option.md`
+  - `docs/config/bump.md`
+- Automation docs:
+  - `docs/tutorials/github_actions.md`
+  - `docs/tutorials/gitlab_ci.md`
+- Error handling:
+  - `docs/exit_codes.md`
+
+## Examples
+
+- Validate one message: `cz check --message "feat(cli): add release command"`
+- Validate branch history: `cz check --rev-range master..HEAD`
+- Preview the next version: `cz bump --get-next`
+- Preview bump details: `cz bump --dry-run`
+- Preview changelog output: `cz changelog --dry-run`
+- Initialize configuration: `cz init`