track_progress should support pull_request 'labeled' action

## Problem

`track_progress: true` fails when the workflow is triggered by a `pull_request: [labeled]` event:

```
Error: Action failed with error: track_progress for pull_request events is only supported for actions: opened, synchronize, ready_for_review, reopened. Current action: labeled
```

## Use case

Using labels as a manual trigger for Claude reviews is a valid and common pattern. Instead of running the review on every PR event (`opened`, `synchronize`), the user adds a label (e.g., `claude`) to explicitly request a review when they want one. This avoids unnecessary API calls and gives the user control over when reviews happen.

Example workflow:

```yaml
on:
pull_request:
types: [labeled]

jobs:
claude-review:
if: ${{ github.event.label.name == 'claude' }}
steps:
- uses: anthropics/claude-code-action@v1
with:
track_progress: true
# ...
```

## Why it should work

The `labeled` event payload contains the same `pull_request.number` and commit SHA as `opened` or `synchronize`. There's no technical reason `track_progress` can't function — it has all the information it needs to post progress updates on the PR.

## Current workaround

Setting `track_progress: false`, which loses the progress indicator.

## Expected behavior

`track_progress: true` should work with `pull_request` events of type `labeled` (and ideally `unlabeled` too, for completeness).

Trace the track_progress handling for pull_request actions, using the reported labeled failure and the example GitHub Actions workflow as the starting point. Support labeled events, and ideally unlabeled events, while preserving progress updates on the pull request; done means the workflow no longer rejects these actions when track_progress is true.

Written by the indexing model from the issue text.