refactor(open-sse): remove dead buildProviderUrl/Headers path (A1)

These translate-path builders had no runtime consumers: the translator route
uses executor.buildUrl/buildHeaders, and the barrel re-exports were unused.
Removing them eliminates the parallel URL/header build path (single source of
truth = executors). Drop their private helpers and the now-unused clineAuth
import. Golden executor snapshots + gate: no regression.

Co-authored-by: Cursor <cursoragent@cursor.com>

open-sse/index.js

@@ -31,8 +31,6 @@ export {
 export { 
   detectFormat, 
   getProviderConfig, 
-  buildProviderUrl, 
-  buildProviderHeaders, 
   getTargetFormat 
 } from "./services/provider.js";