feat(workflows): add local event store mode to Vision Events block (ENT-1192) (#2402)

Add a "Write to Local Event Store" toggle to the Roboflow Vision Events block so
one block serves both cloud (Serverless API) and edge deployments, removing the
need to swap between it and the enterprise Event Writer block.

When enabled, the block embeds images as base64 and POSTs to a local Event
Ingestion Service (<event store URL>/v2/events, default http://localhost:8001)
instead of the cloud Vision Events API. No Roboflow API key is required in this
mode; the local service is authenticated via EVENT_INGESTION_API_KEY.

- New manifest fields: write_to_event_store (advanced) and event_store_url
  (revealed via relevant_for when the toggle is on)
- Forwards `solution` and supports all event schemas incl. operator_feedback
- Adds event_id output: cloud returns the client-generated UUID, local parses
  the service-assigned id from the 201 response (mirrors Event Writer)
- Mirrors Event Writer 201/529 response handling for the shared endpoint
- requires_rf_key -> False so the block is configurable in the edge-embedded editor
- Event Writer block left unchanged

Validated end-to-end against a local Event Ingestion Service; 47 unit tests pass.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Co-authored-by: Paweł Pęczek <146137186+PawelPeczek-Roboflow@users.noreply.github.com>

Author: 3 people