Add: typed Flow render props

[bcheung]

Why This Feature?

Improve the React Flow render-prop API so step IDs and navigation targets are inferred from the flow definition instead of falling back to broad string types.

Implementation

• Types Flow render-prop callbacks from the provided flow definition.
• Narrows next, skip, and explicit navigation targets by the current step.
• Preserves step-local render-prop target types through the React package exports.
• Adds type tests covering inferred step IDs and allowed navigation targets.
• Updates docs and examples for the typed Flow API and routing guidance.
• Adds a Changesets minor release entry.

Testing

• Commit hook typecheck passed
• Pre-push typecheck passed
• Pre-push test suite passed: 17 files, 344 tests
• bun run changeset status --verbose
• Changesets reports @useflow/core@0.3.0 and @useflow/react@0.3.0

Screenshots

N/A

Related

After merge, the release workflow should create a Version Packages PR. Merging that PR will publish aligned 0.3.0 versions for both packages.