feat(i18n): persist language preference and thread through chat, memoir, TTS

- Add users.language_preference (Alembic 0018, default zh); capture at signup/SMS
  only; expose on auth and profile APIs
- Lite English prompts for chat and memoir; localized stage labels and agent
  names (Life Echo / 岁月知己)
- Tencent TTS: language-aware synthesis, ModelType=1 for 501004, English chunking
- WebSocket pipeline: emit all AGENT_RESPONSE segments when TTS cancels; INFO logs
  for tts_this_turn and TTS decisions; on-demand TTS logging
- Expo: device language on auth, i18n tiers/agent name, [SPLIT] streaming UX fixes
- Tests for migration, prompts, pipeline, router tts_this_turn, reply segments

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

api/app/agents/memoir/narrative_agent.py

@@ -13,7 +13,7 @@ from app.agents.memoir.prompts import (
     get_narrative_merge_json_prompt,
 )
 from app.agents.memoir.schemas import MemoirTitleOutput
-from app.agents.stage_constants import CHAPTER_CATEGORIES
+from app.agents.stage_constants import CHAPTER_CATEGORIES, chapter_category_display
 from app.core.config import settings
 from app.core.langchain_llm import invoke_json_object
 from app.core.llm_call import llm_json_call
@@ -22,6 +22,13 @@ from app.core.logging import get_logger
 logger = get_logger(__name__)
 
 
+def _default_title_for(stage: str, language: str) -> str:
+    if language == "en":
+        cat = chapter_category_display(stage, language="en") or stage
+        return f"{cat} Memory"
+    return f"{CHAPTER_CATEGORIES.get(stage, stage)} 回忆"
+
+
 class NarrativeAgent:
     """生成章节标题和叙事正文"""
 
@@ -33,10 +40,11 @@ class NarrativeAgent:
         user_profile: str = "",
         birth_year: Optional[int] = None,
         llm: Any = None,
+        language: str = "zh",
     ) -> str:
         """生成创意标题。若无 LLM 则返回默认标题"""
         if not llm:
-            return f"{CHAPTER_CATEGORIES.get(stage, stage)} 回忆"
+            return _default_title_for(stage, language)
         try:
             prompt = get_creative_title_json_prompt(
                 stage=stage,
@@ -44,8 +52,9 @@ class NarrativeAgent:
                 slots=slots,
                 user_profile=user_profile,
                 birth_year=birth_year,
+                language=language,
             )
-            default_title = f"{CHAPTER_CATEGORIES.get(stage, stage)} 回忆"
+            default_title = _default_title_for(stage, language)
 
             def _title_fallback() -> MemoirTitleOutput:
                 return MemoirTitleOutput(title=default_title)
@@ -64,7 +73,7 @@ class NarrativeAgent:
             return default_title
         except Exception as e:
             logger.warning("NarrativeAgent 生成标题失败: {}", e)
-            return f"{CHAPTER_CATEGORIES.get(stage, stage)} 回忆"
+            return _default_title_for(stage, language)
 
     def generate_narrative(
         self,
@@ -79,6 +88,7 @@ class NarrativeAgent:
         occupation: str = "",
         *,
         fallback_plain_oral: str = "",
+        language: str = "zh",
     ) -> str:
         """将新对话改写为叙述。若无 LLM 则直接拼接。
 
@@ -106,6 +116,7 @@ class NarrativeAgent:
                     birth_year=birth_year,
                     background_voice=background_voice,
                     occupation=occupation,
+                    language=language,
                 )
                 max_tokens = int(settings.memoir_narrative_merge_max_tokens)
                 agent_name = "NarrativeAgent.generate_narrative_merge"
@@ -119,6 +130,7 @@ class NarrativeAgent:
                     birth_year=birth_year,
                     background_voice=background_voice,
                     occupation=occupation,
+                    language=language,
                 )
                 max_tokens = int(settings.memoir_narrative_max_tokens)
                 agent_name = "NarrativeAgent.generate_narrative"