refactor(open-sse): D1c — forceStream hardcode → PROVIDERS schema (#5)

chatCore providerRequiresStreaming: switch provider-name →
PROVIDERS[provider].forceStream. Thêm forceStream:true vào registry
openai/codex/commandcode. verify-providers allowlist added-fields
(forceStream/urlSuffix verified bằng golden + runtime test riêng).

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

open-sse/providers/registry/openai.js

@@ -2,7 +2,8 @@ export default {
   "id": "openai",
   "alias": "openai",
   "transport": {
-    "baseUrl": "https://api.openai.com/v1/chat/completions"
+    "baseUrl": "https://api.openai.com/v1/chat/completions",
+    "forceStream": true
   },
   "models": [
     {