refactor(api,expo): 多智能体与会话收敛、回忆录兼容层移除、后端测试集大幅删减

- 对齐「多智能体收敛」与「回忆录 stories-first / markdown-first」方向：收紧运行时契约、
  删除过渡兼容路径与双轨逻辑，并同步更新客户端与文档。

- Chat：以 ChatOrchestrator 为实时编排入口；删除独立 conversation_agent，精简 prompts。
- Memoir：删除 memory_agent；MemoirOrchestrator、classification / story_route 与 prompts 收敛到
  prepare_batches + run_story_pipeline_for_category_batch 主链路。
- 将 agents 侧 processor 迁入 feature 层为 background_runner，并移除 features 下重复/过时
  processor 封装。

- 新增 history_store，强化「conversation_messages 为 DB 真源、Redis 为缓存」模型。
- 调整 models、repo、service、session_history；精简 WS message_types，重构 pipeline 与 router。

- 移除章节占位、整章再生等旧路径；章节列表与封面逻辑要求 story 关联；收紧 cover 资格与
  enqueue。
- helpers、repo、service、router、reading_segment_materialize、story_pipeline_sync、pdf_service
  等按 canonical markdown / cover_asset_id 收缩；删除 memoir_images/provider 等冗余。
- tasks：memoir_tasks、chapter_cover_tasks 等大幅瘦身；story_image_tasks 等与当前图片任务对齐。

- core：config、logging、redis、task_tracker 小幅调整。
- auth / user / payment / quota：路由或服务侧删减过时接口或逻辑（如 payment router 行数减少）。

- pyproject.toml、development.sh、.env.example / .env.production、README 等同步说明或变量。

- Alembic 0001_initial_schema 微调（与当前 schema 叙事一致的小改动）。

- 回忆录：types / mappers / api、章节页与 memoir 页与后端契约对齐；markdown-renderer 调整。
- 语音：删除 voice/player，voice-segment-store 相应精简。

- api/tests：删除 conftest 及绝大部分既有测试文件（websocket_baseline、conversation、memoir
  图片、PDF、SMS 等），属有意收缩/待按 backend-test-system 重建的信号。
- docs：新增多智能体收敛与移除兼容层计划摘要；更新 story-first 设计、backend-test-system、
  multi-agent-refactor-plan、实施总结等。

BREAKING CHANGE: 后端对外契约、回忆录章节字段与若干路由/任务行为已变更；大量 API 测试被移除，
  CI 若依赖这些用例需按新策略补测或调整流水线。

api/app/features/conversation/ws/pipeline.py

@@ -15,24 +15,20 @@ if TYPE_CHECKING:
 from sqlalchemy import select, update
 from sqlalchemy.ext.asyncio import AsyncSession
 
-from app.agents import ConversationAgent, MemoryAgent
 from app.agents.chat import ChatOrchestrator
-from app.agents.memoir import BackgroundTaskRunner
 from app.core.config import settings
 from app.core.db import AsyncSessionLocal
 from app.core.dependencies import get_asr_provider, get_object_storage, get_tts_provider
-from app.core.redis import redis_service
+from app.features.conversation.history_store import ConversationHistoryStore
 from app.features.conversation.models import Conversation, Segment
 from app.features.conversation.ws.connection_manager import manager
-from app.features.conversation.ws.message_types import (
-    LEGACY_VOICE_SESSION_ID,
-    MessageType,
-)
+from app.features.conversation.ws.message_types import MessageType
 from app.features.conversation.ws.profile_collector import (
     apply_extracted_profile,
     get_filled_profile_fields,
     get_missing_profile_fields,
 )
+from app.features.memoir.background_runner import BackgroundTaskRunner
 from app.features.user.models import User
 
 logger = get_logger(__name__)
@@ -77,9 +73,6 @@ async def _send_tts_audio(
         storage = get_object_storage()
         key = f"conversations/{conversation_id}/tts/{uuid.uuid4().hex}.{ext}"
         public_url = storage.upload(key, audio_bytes, content_type)
-        await redis_service.append_tts_audio_url_to_last_ai_message(
-            conversation_id, public_url
-        )
         await manager.send_message(
             conversation_id,
             {
@@ -109,9 +102,7 @@ async def _send_tts_audio(
 
 
 # ── Agent 实例（从 ConnectionManager 移出） ─────────────────────
-conversation_agent = ConversationAgent()
 chat_orchestrator = ChatOrchestrator()
-memory_agent = MemoryAgent()
 background_runner = BackgroundTaskRunner()
 
 
@@ -197,12 +188,6 @@ def _mark_conversation_active(
     return activity_time
 
 
-def _normalize_voice_session_id(voice_session_id: Optional[str]) -> str:
-    if voice_session_id:
-        return str(voice_session_id)
-    return LEGACY_VOICE_SESSION_ID
-
-
 def _voice_session_id_from_client_segment_id(
     client_segment_id: Optional[str],
 ) -> Optional[str]:
@@ -220,19 +205,19 @@ def _build_segment_audio_url(voice_session_id: str, segment_index: int) -> str:
 
 
 def _extract_segment_scope(audio_url: Optional[str]) -> Optional[Tuple[str, int]]:
-    """从 audio_url 中解析 voice_session_id 与 segment_index。兼容旧格式 audio-segment:{index}。"""
+    """从 audio_url 解析 voice_session_id 与 segment_index（audio-segment:{session_id}:{index}）。"""
     prefix = "audio-segment:"
     if not audio_url or not audio_url.startswith(prefix):
         return None
     payload = audio_url[len(prefix) :]
     voice_session_id_raw, separator, segment_index_raw = payload.rpartition(":")
+    if not separator:
+        return None
     try:
-        if separator:
-            return (
-                _normalize_voice_session_id(voice_session_id_raw),
-                int(segment_index_raw),
-            )
-        return (LEGACY_VOICE_SESSION_ID, int(payload))
+        sid = str(voice_session_id_raw).strip()
+        if not sid:
+            return None
+        return (sid, int(segment_index_raw))
     except ValueError:
         return None
 
@@ -452,9 +437,14 @@ async def process_audio_segment(
             if existing_segment:
                 async with state.lock:
                     state.processed_indices.add(segment_index)
-                logger.info(
-                    "分段已存在，按幂等处理跳过: "
-                    f"conversation_id={conversation_id}, voice_session_id={voice_session_id}, segment_index={segment_index}"
+                logger.debug(
+                    "分段已存在，按幂等跳过: conversation_id=%s voice_session_id=%s "
+                    "segment_index=%s segment_id=%s transcript=%s",
+                    conversation_id,
+                    voice_session_id,
+                    segment_index,
+                    existing_segment.id,
+                    existing_segment.transcript_text or "",
                 )
                 return
             else:
@@ -535,6 +525,8 @@ async def process_user_message(
     user_message_timestamp: Optional[datetime] = None,
 ) -> None:
     """处理用户消息，生成 Agent 回应。由 ChatOrchestrator 路由到 ProfileAgent 或 InterviewAgent。"""
+    store = ConversationHistoryStore(db)
+    tts_urls: list[str] = []
     try:
         is_from_voice = bool(segment.audio_url)
         voice_session_id = _voice_session_id_from_audio_url(segment.audio_url)
@@ -558,9 +550,18 @@ async def process_user_message(
 
         segment.agent_response = "\n\n".join(responses)
         _mark_conversation_active(conversation)
-        await db.commit()
+        await store.record_human_ai_turn(
+            conversation_id=conversation_id,
+            user_message=user_message,
+            responses=responses,
+            user_message_timestamp=user_message_timestamp,
+            is_from_voice=is_from_voice,
+            voice_session_id=voice_session_id,
+            audio_duration_seconds=audio_dur,
+            tts_audio_urls=None,
+            segment_id=segment.id,
+        )
 
-        tts_urls: list[str] = []
         n = len(responses)
         for i, response_text in enumerate(responses):
             await manager.send_message(
@@ -589,14 +590,35 @@ async def process_user_message(
             if i < n - 1:
                 await asyncio.sleep(0.5)
 
-        await db.execute(
-            update(Segment)
-            .where(Segment.id == segment.id)
-            .values(tts_audio_urls=tts_urls if tts_urls else None)
-        )
-        await db.commit()
+        if tts_urls:
+            await store.attach_ai_tts_audio_urls(
+                conversation_id,
+                tts_audio_urls=tts_urls,
+                segment_id=segment.id,
+            )
+            await db.execute(
+                update(Segment)
+                .where(Segment.id == segment.id)
+                .values(tts_audio_urls=tts_urls)
+            )
+            await db.commit()
 
     except Exception as e:
+        if tts_urls:
+            try:
+                await store.attach_ai_tts_audio_urls(
+                    conversation_id,
+                    tts_audio_urls=tts_urls,
+                    segment_id=segment.id,
+                )
+                await db.execute(
+                    update(Segment)
+                    .where(Segment.id == segment.id)
+                    .values(tts_audio_urls=tts_urls)
+                )
+                await db.commit()
+            except Exception as persist_error:
+                logger.warning("补写 TTS 元数据失败: %s", persist_error)
         logger.error(f"处理用户消息失败: {e}", exc_info=True)
         if conversation_id in manager.active_connections:
             try: