Add SSE streaming endpoints to HttpApi

Normalized profile

What this task asks for

Add typed Server-Sent Events streaming endpoints, encoders/decoders, and client handling to HttpApi. The HttpApi framework should support endpoints that produce typed event streams via SSE. Only sse() marks an endpoint as SSE. Support Schema.TaggedClass and wrapped (including transformed) or suspended union members when extracting union member tags. FormatMessage(msg) returns an SSE wire-format string with multi-line data support. SSE endpoints return a Stream instead of a plain value. The client must validate response status before streaming so error responses still fail the outer Effect.