Detect issue and pull request templates

[andrew]

Report issue and pull request templates under resources.templates so that contributors and coding agents can find and follow them when opening issues or PRs.

Detection covers the locations recognised by GitHub, GitLab, Gitea, and Forgejo: repo root, docs/, .github/, .gitea/, .forgejo/, and .gitlab/. Both single-file templates (PULL_REQUEST_TEMPLATE.md, issue_template.md) and directory forms (ISSUE_TEMPLATE/, PULL_REQUEST_TEMPLATE/, GitLab issue_templates/ and merge_request_templates/) are picked up. The issue chooser config.yml is reported separately under templates.config since it is not itself a template. GitLab merge request templates are folded into pull_request rather than getting their own field.

This is special-cased in the detection engine rather than driven by _resources.toml because the existing resource matcher returns a single path per field and skips directories, whereas templates are inherently a list and the directory form is the common case on GitHub.

Output looks like:

"resources": {
  "templates": {
    "issue": [
      ".github/ISSUE_TEMPLATE/bug.md",
      ".github/ISSUE_TEMPLATE/feature.yml"
    ],
    "pull_request": [
      ".github/PULL_REQUEST_TEMPLATE.md"
    ],
    "config": ".github/ISSUE_TEMPLATE/config.yml"
  }
}