feat(builders): add after-bundle hook

[lucamaraschi]

Adds an awaited onAfterBundle hook to @workflow/builders.

The hook runs after a successful workflow bundle and manifest build and provides:

• The build target and working directory
• The generated workflow manifest
• Absolute paths for the steps bundle, workflows bundle, and manifest
• Consistent invocation after successful watch rebuilds, including when the manifest contents are unchanged

Hook errors propagate to the caller. Failed or incomplete bundle and manifest builds do not invoke the hook.

This enables integrations to consume completed workflow build artifacts without reproducing the builder lifecycle internally.

Nitro-specific integration is intentionally excluded and will be handled separately.

How did you test your changes?

• Added coverage using the real combined-bundle and manifest lifecycle
• Verified invocation after successful watch rebuilds
• Verified relative manifest directories report the actual written path
• Verified the hook is awaited and errors propagate
• Verified failed bundle and manifest builds do not invoke the hook
• Built and typechecked @workflow/builders
• Ran the complete builders test suite: 243 tests passed

PR Checklist - Required to merge

• 📦 Added a minor changeset for @workflow/builders
• 🔒 Commit includes the required DCO Signed-off-by trailer
• 📝 Ping @vercel/workflow once the PR is ready for review

[changeset-bot]

🦋 Changeset detected

Latest commit: 25a8465

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 16 packages

Name	Type
@workflow/builders	Minor
@workflow/astro	Patch
@workflow/cli	Patch
@workflow/nest	Patch
@workflow/next	Patch
@workflow/nitro	Patch
@workflow/rollup	Patch
@workflow/sveltekit	Patch
@workflow/vite	Patch
@workflow/vitest	Patch
workflow	Patch
@workflow/world-testing	Patch
@workflow/nuxt	Patch
@workflow/core	Patch
@workflow/web-shared	Patch
@workflow/web	Patch

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[vercel]

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