Consumer-facing price check interface

A new public /price-check page lets anyone query live multi-modal pricing without signing in. Results stream through the public pipelines endpoint with a 2 MB body cap.

Anyone can now visit `/price-check` to run a live pricing query across modalities, no account required. The page is linked from the main nav and uses a streaming pipeline endpoint purpose-built for public access.

New `/price-check` page with a multi-modal pricing form available to all visitors

Public pipelines API endpoint enforces a 2 MB request body limit

Abort handling cancels in-flight requests when the user navigates away