docs: add data source flow guide and localize handoff READMEs

- Add docs/DATA_SOURCE_FLOW.md: end-to-end source -> NotebookLM ->
  storage -> App flow, source list with publish frequency, institution
  intro status, ingestion artifact structure, and known cadence gaps
- Link the new doc from README and PROJECT_OVERVIEW indexes
- Localize top-level and subproject READMEs to Chinese for handoff
  (pre-existing working-tree changes)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

report-notebooklm-api/README.md

@@ -1,30 +1,30 @@
 # report-notebooklm-api
 
-FastAPI service for the report-notebooklm Phase 1 public read surface.
+report-notebooklm 第一阶段对外只读接口的 FastAPI 服务。
 
-This directory is the main engineering handoff entry for API, data model, seed import, and the NotebookLM-backed content pipeline. The companion Flutter app lives in `../report-notebooklm-app/` in the same monorepo.
+这个目录是 API、数据模型、种子数据导入，以及由 NotebookLM 支撑的内容流水线的主要工程交接入口。配套的 Flutter 应用在同一个 monorepo 的 `../report-notebooklm-app/` 里。
 
-## Read First
+## 先读这些
 
-- [docs/HANDOFF.md](docs/HANDOFF.md): current progress, solved issues, open issues, and handoff order.
-- [docs/PROJECT_BRIEF.md](docs/PROJECT_BRIEF.md): product and Phase 1 scope snapshot.
-- [docs/API_AND_DATA.md](docs/API_AND_DATA.md): data tables, endpoints, implemented vs planned API.
-- [docs/CONTENT_PIPELINE.md](docs/CONTENT_PIPELINE.md): report source and NotebookLM artifact flow.
-- [docs/RUNBOOK.md](docs/RUNBOOK.md): local setup, seed import, smoke checks, and deployment checks.
-- [docs/ROADMAP_AND_OPEN_ISSUES.md](docs/ROADMAP_AND_OPEN_ISSUES.md): next engineering work.
-- [docs/SOURCE_INDEX.md](docs/SOURCE_INDEX.md): source document names used for this handoff snapshot.
+- [docs/HANDOFF.md](docs/HANDOFF.md)：当前进度、已解决的问题、待解决的问题，以及交接顺序。
+- [docs/PROJECT_BRIEF.md](docs/PROJECT_BRIEF.md)：产品和第一阶段范围速览。
+- [docs/API_AND_DATA.md](docs/API_AND_DATA.md)：数据表、接口，以及已实现 / 计划中的 API。
+- [docs/CONTENT_PIPELINE.md](docs/CONTENT_PIPELINE.md)：研报来源和 NotebookLM 产物的流转。
+- [docs/RUNBOOK.md](docs/RUNBOOK.md)：本地搭建、种子数据导入、冒烟检查和部署检查。
+- [docs/ROADMAP_AND_OPEN_ISSUES.md](docs/ROADMAP_AND_OPEN_ISSUES.md)：下一步的工程工作。
+- [docs/SOURCE_INDEX.md](docs/SOURCE_INDEX.md)：本次交接快照所用到的源文档名称。
 
-## Product Boundary
+## 产品边界
 
-This repo contains code and an engineering handoff snapshot. It is not the product source of truth.
+这个仓库装的是代码和一份工程交接快照，不是产品的唯一真源。
 
-Product SSOT: mall-docs report-notebooklm docs. Snapshot date: 2026-06-03.
+产品 SSOT：mall-docs 里的 report-notebooklm 文档。快照日期：2026-06-03。
 
-Use `report-notebooklm` and `rnb` for technical identifiers. The user-facing product name is `研听`.
+技术标识符用 `report-notebooklm` 和 `rnb`，面向用户的产品名是 `研听`。
 
-## Local Quick Start
+## 本地快速上手
 
-Create a `.env` file with the backend services available to your environment:
+按你环境里可用的后端服务，创建一个 `.env` 文件：
 
 ```bash
 RNB_DATABASE_URL=mysql+asyncmy://<db-user>:<db-pass>@<db-host>:<db-port>/report_notebooklm
@@ -32,7 +32,7 @@ RNB_REDIS_URL=redis://<host>:<port>/0
 RNB_REDIS_KEY_PREFIX=rnb:
 ```
 
-Then run:
+然后运行：
 
 ```bash
 python -m venv .venv
@@ -43,16 +43,16 @@ python scripts/import_seed_content.py
 uvicorn app.main:app --reload --host <bind-host> --port <port>
 ```
 
-API prefix: `/api/report-notebooklm/v1`
+API 前缀：`/api/report-notebooklm/v1`
 
-## Verify
+## 验证
 
 ```bash
 source .venv/bin/activate
 pytest -q
 ```
 
-Recommended smoke checks after the service starts:
+服务启动后，建议做这些冒烟检查：
 
 ```bash
 API_BASE_URL=http://<api-host>:<port>/api/report-notebooklm/v1