[Workflows] add subscribe documentation and changelog

[mkuritsu]

Summary

This PR adds documentation and changelog entry for the new workflows subscribe feature.

Documentation checklist

• Is there a changelog entry (guidelines)? If you don't add one for something awesome and new (however small) — how will our customers find out? Changelogs are automatically posted to RSS feeds, the Discord, and X.
• The change adheres to the documentation style guide.

[cloudflare-docs-bot]

Review

⚠️ 1 warning found in commit 86001dc.

👉 Fix in your agent 👈

Fix the following review findings in PR #33361 (https://github.com/cloudflare/cloudflare-docs/pull/33361).

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---

## Code Review

### Warnings (1)

#### CR-637d8152e80a · Incorrect API description
- **File:** `src/content/docs/workflows/build/workers-api.mdx` line 775
- **Issue:** The text claims each `next()` call "returns the next matching `WorkflowInstanceEvent`". The sibling page added in this PR (`subscribe-to-instance-events.mdx`) shows `next()` returns an async-iterator result: `const result = await subscription.next(); if (result.done) break; console.log(result.value.type, ...)`. Following this wording, a user would treat the result directly as the event (e.g. `event.type`) instead of `result.value.type`, producing undefined fields.
- **Fix:** Reword to say each `next()` call returns the next iterator result (`{ done, value }`) whose `value` is the matching `WorkflowInstanceEvent`, matching the examples in the linked Subscribe to events page.

Code Review

This code review is in beta and may not always be helpful — use your judgment.

Warnings (1)

File

Issue

workflows/build/workers-api.mdx line 775

Incorrect API description — The text claims each next() call "returns the next matching WorkflowInstanceEvent". The sibling page added in this PR (subscribe-to-instance-events.mdx) shows next() returns an async-iterator result: const result = await subscription.next(); if (result.done) break; console.log(result.value.type, ...). Following this wording, a user would treat the result directly as the event (e.g. event.type) instead of result.value.type, producing undefined fields. Fix: Reword to say each next() call returns the next iterator result ({ done, value }) whose value is the matching WorkflowInstanceEvent, matching the examples in the linked Subscribe to events page.

Conventions

_{No convention issues found.}

Style Guide Review

_{No style-guide issues found.}

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