[oblt-aw][autodoc] Fix actionable documentation errors in action READMEs

cc `@elastic/observablt-ci`

Recent documentation audit found concrete, user-impacting drift in multiple action READMEs.

## Changes Requiring Documentation Updates

### 1. `snapshoty/run` usage example uses an invalid input key

**Evidence:**
- `snapshoty/run/action.yml:13` defines required input `gcs-private-key`
- `snapshoty/run/README.md:35` uses `gcs-private-ley`

**Documentation impact:**
The usage snippet is copy/paste broken and will fail with an unknown input.

### 2. `github/comment-reaction` README includes invalid workflow YAML

**Evidence:**
- `github/comment-reaction/README.md:33` has incomplete expression: `if: $\{\{ github.event.issue.pull_request`
- `github/comment-reaction/README.md:34` uses `permission:` instead of valid `permissions:`

**Documentation impact:**
Published usage example is syntactically invalid and not runnable.

### 3. `slack/send` README omits a documented action output

**Evidence:**
- `slack/send/action.yml:29-32` defines output `thread-timestamp`
- `slack/send/README.md` has `Inputs` and `Usage` sections but no `Outputs` section

**Documentation impact:**
Consumers cannot discover/document how to reuse `thread-timestamp` for threaded replies.

### 4. `github/create-token` README test badge points to a different action workflow

**Evidence:**
- `github/create-token/README.md:5` links to `test-github-user-type.yml`
- `.github/workflows/test-github-create-token.yml:1` is the correct create-token workflow

**Documentation impact:**
Cross-reference is misleading and does not represent create-token test status.

## Suggested Actions

- [ ] In `snapshoty/run/README.md`, replace `gcs-private-ley` with `gcs-private-key` and re-validate usage against `action.yml` inputs.
- [ ] In `github/comment-reaction/README.md`, fix the `if` expression and rename `permission:` to `permissions:` in the workflow snippet.
- [ ] In `slack/send/README.md`, add an `## Outputs` section documenting `thread-timestamp` and include a usage reference to `$\{\{ steps.(id).outputs.thread-timestamp }}`.
- [ ] In `github/create-token/README.md`, update the test badge link/text to `test-github-create-token.yml`.

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[What is this?](https://ela.st/github-ai-tools) | [From workflow: Observability Agentic Workflow Entrypoint](https://github.com/elastic/oblt-actions/actions/runs/23703146640)

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