Fix dist/run.js missing from repo: anchor root gitignore dist rule

Root .gitignore had `dist/` which recursively excluded the action's
committed bundle at .github/actions/report/dist/run.js. Changed to
`/dist/` to anchor the rule to the repo root only (Worker build output),
leaving the Action bundle trackable.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: tbjers