docs: add workflow import migration note to README

[flora131]

Summary

Adds a temporary warning to the root README alerting users to a breaking change in workflow authoring that may require updates to custom workflows using the old import API.

Key Changes

• Added a ⚠️ callout block in the README's workflow section noting that custom workflows importing other workflows by registered name or path object need to be migrated
• Points users to the workflow import guidance in packages/workflows/README.md for migration instructions

Migration Context

This note accompanies the breaking change introduced in #1181 (feat(workflows)!: TypeBox-native input/output schemas). Workflow imports now use standard TypeScript module imports and pass compiled workflow definitions to .import(workflow, { as? }) rather than importing by registered name or path object.

[claude]

Review

Thanks for adding the migration note — a heads-up here is helpful for anyone who maintains custom workflows. The PR is tiny and low-risk (README-only, no code), but flagging two issues that should be fixed in a follow-up:

1. Broken anchor link

The link targets #example-4--compose-workflows-with-imports, but the actual heading in packages/workflows/README.md:144 is:

### Example 4 — Compose workflows

GitHub renders that heading's anchor as #example-4--compose-workflows (em-dash dropped, surrounding spaces collapse into a double hyphen). The trailing -with-imports is not in the heading, so this link currently 404s within the target README.

Fix: either update the link to #example-4--compose-workflows, or rename the section in packages/workflows/README.md to ### Example 4 — Compose workflows with imports so the link resolves.

2. API name in the note doesn't match the documented API

The note says:

Workflow imports now use normal TypeScript module imports and pass compiled workflow definitions to .import(workflow, { as? }).

But the workflows README (and the surrounding Example 4 body) describes the API as ctx.workflow(workflowDefinition, options) — see packages/workflows/README.md:146 and :204. A grep of packages/workflows/src/ finds no .import( method either. Users who try to call .import(...) after reading this note won't find it.

Fix: rephrase to refer to ctx.workflow(workflowDefinition, { as? }) (or whatever the actual aliasing option key is) so the note matches the documented surface it links to.

Other categories

• Performance / security / tests: N/A — docs-only change.
• Style: consistent with the existing callout block above it. ✅

Once the anchor and the API name are corrected, the migration note will do its job. Small follow-up PR recommended since this already merged.