docs(hooks): document hook payload fields

[tt-a1i]

Related Issue

Resolve #917
Resolve #916

Problem

See linked issue.

What changed

• Clarified that UserPromptSubmit matchers run against text extracted from submitted content parts.
• Documented that hook stdin receives prompt: ContentPart[], including text and media content parts, rather than a plain string.
• Added a per-event stdin payload field table for hook authors.
• Kept the English and Chinese hooks docs in sync.

Checklist

• I have read the CONTRIBUTING document.
• I have linked a related issue, or explained the problem above.
• Docs-only change; validated with VitePress build.
• Ran gen-changesets skill, or this PR needs no changeset.
• Ran gen-docs skill, or this PR needs no doc update.

[changeset-bot]

⚠️ No Changeset found

Latest commit: e35fb72

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes no changesets

When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types

Click here to learn what changesets are, and how to add one.

Click here if you're a maintainer who wants to add a changeset to this PR