feat: streaming (SSE) end-to-end

- Provider::chat_stream; OpenAI provider streams via stream_options.include_usage
- pipeline.run_stream: shared route/select, failover before first byte
- /v1/chat/completions forwards SSE verbatim with X-Cortiq-* headers; usage tapped for stats
- admin /test/stream + live streaming in Playground (stream toggle, 7 langs)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

web/js/i18n/de.js

@@ -200,6 +200,7 @@ export default {
   "pg.temp": "Temperatur",
   "pg.maxTokens": "Max. Tokens",
   "pg.send": "Senden",
+  "pg.stream": "Streamen",
   "pg.sending": "Wird gesendet…",
   "pg.answer": "Antwort",
   "pg.empty": "Antwort und Routing-Entscheidung erscheinen hier.",

web/js/i18n/en.js

@@ -201,6 +201,7 @@ export default {
   "pg.temp": "Temperature",
   "pg.maxTokens": "Max tokens",
   "pg.send": "Send",
+  "pg.stream": "Stream",
   "pg.sending": "Sending…",
   "pg.answer": "Answer",
   "pg.empty": "The answer and routing decision will appear here.",

web/js/i18n/es.js

@@ -200,6 +200,7 @@ export default {
   "pg.temp": "Temperatura",
   "pg.maxTokens": "Tokens máx.",
   "pg.send": "Enviar",
+  "pg.stream": "Streaming",
   "pg.sending": "Enviando…",
   "pg.answer": "Respuesta",
   "pg.empty": "La respuesta y la decisión de enrutamiento aparecerán aquí.",

web/js/i18n/fr.js

@@ -200,6 +200,7 @@ export default {
   "pg.temp": "Température",
   "pg.maxTokens": "Tokens max",
   "pg.send": "Envoyer",
+  "pg.stream": "Streaming",
   "pg.sending": "Envoi…",
   "pg.answer": "Réponse",
   "pg.empty": "La réponse et la décision de routage s'afficheront ici.",

web/js/i18n/ru.js

@@ -200,6 +200,7 @@ export default {
   "pg.temp": "Температура",
   "pg.maxTokens": "Макс. токены",
   "pg.send": "Отправить",
+  "pg.stream": "Стриминг",
   "pg.sending": "Отправка…",
   "pg.answer": "Ответ",
   "pg.empty": "Ответ и решение роутера появятся здесь.",

web/js/i18n/tr.js

@@ -200,6 +200,7 @@ export default {
   "pg.temp": "Sıcaklık",
   "pg.maxTokens": "Maks. token",
   "pg.send": "Gönder",
+  "pg.stream": "Akış",
   "pg.sending": "Gönderiliyor…",
   "pg.answer": "Yanıt",
   "pg.empty": "Yanıt ve yönlendirme kararı burada görünecek.",

web/js/i18n/zh.js

@@ -200,6 +200,7 @@ export default {
   "pg.temp": "温度",
   "pg.maxTokens": "最大 Token 数",
   "pg.send": "发送",
+  "pg.stream": "流式",
   "pg.sending": "发送中…",
   "pg.answer": "回答",
   "pg.empty": "回答和路由决策将在此显示。",