Support full role permission checks

[Pybsama]

Summary

• match the full collaborator role_name as well as the legacy base permission
• allow maintain-only configurations to distinguish maintainers from ordinary writers
• preserve existing write/admin compatibility, document the behavior, and rebuild the Action bundle

This intentionally matches either API field: GitHub maps maintain to write and triage to read in the legacy permission field, so replacing that field outright would break existing base-permission configurations.

Tests

• npm run test — 12 suites, 106 tests, 100% line coverage
• npm run all
• npm run format-check

Fixes #101

[Pybsama]

Revalidated this PR against current main on 2026-08-31:

• Upstream main is still 3442f3fa; the public PR head is b592cf04, and GitHub's synthetic merge tree exactly matches the tested head tree (f4e2697b).
• RED check: restoring the original base-permission-only implementation produces 4 failures and 9 passes in the 13 authorization tests, covering maintain, triage, custom roles, and the full-role diagnostic.
• GREEN check: 13/13 authorization tests pass, including 50 consecutive focused runs.
• Node 22.13.1 / npm 10.9.2: 12/12 suites and 106/106 tests pass. Statements, functions, and lines are 100%; valid-permissions.js also has 100% branch coverage.
• Prettier, ESLint, npm run all, git diff --check, and Node syntax validation of the committed bundle pass.
• Two clean ncc rebuilds produced byte-identical dist/index.js, source map, and license hashes with no repository diff.
• The workflow-pinned json-yaml-validate commit validates all four repository JSON files and action.yml against the repository schema.
• Semgrep ran 68 JavaScript rules over the changed source and tests with 0 findings.

npm test also completes all 106 tests, but the currently locked badge generator rewrites styling in the existing coverage SVG. This PR changes neither the badge nor dependencies, so I restored that unrelated generated-file drift; the CI test workflow uses npm run ci-test.

With the implementation, bundle, and current merge tree verified, I am marking this PR ready for review.