A PR that only touches `uv.lock` currently gets the label of its' dir
because the file rule matches on the file prefix. This is misleading —
lockfile-only changes aren't meaningful package changes. The
`excludedFiles` list already existed in config (for size calculations),
but file rules didn't consult it.
## Changes
- Add `skipExcludedFiles` option to file rules in
`pr-labeler-config.json`, enabled for the four package rules
(`deepagents`, `cli`, `acp`, `evals`) so lockfile-only PRs don't trigger
package labels
- `matchFileLabels` in `pr-labeler.js` now filters out files whose
basename appears in the top-level `excludedFiles` list (currently just
`uv.lock`) before testing rules that opt in via `skipExcluded`
- Non-package rules (`github_actions`, `dependencies`) are unaffected —
they don't set the flag
Consolidate four separate PR labeling workflows (`pr_labeler_file.yml`,
`pr_labeler_title.yml`, `pr_size_labeler.yml`, and the PR-handling half
of `tag-external-contributions.yml`) into a single `pr_labeler.yml`
workflow. The old workflows raced against each other — concurrent label
mutations could drop or duplicate labels depending on execution order. A
unified workflow with concurrency grouping eliminates that class of bug.
