chore: prepare yanting monorepo handoff

docs/PROJECT_OVERVIEW.md

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+# Project Overview
+
+This is a handoff snapshot, not the product SSOT.
+
+Product SSOT: mall-docs report-notebooklm docs, snapshot date: 2026-06-03.
+
+## Purpose
+
+`研听` is a Chinese app for understanding global institutional research reports. It converts difficult English research reports into reviewed Chinese reading and listening experiences.
+
+The product is a research-report interpretation and annotation service. It does not provide investment advice.
+
+## Technical Shape
+
+| Layer | Technology | Path |
+|---|---|---|
+| App | Flutter | `report-notebooklm-app/` |
+| API | FastAPI | `report-notebooklm-api/` |
+| Database | MySQL 8 | configured by `RNB_DATABASE_URL` |
+| Cache | Redis | configured by `RNB_REDIS_URL` |
+| Storage | Object storage | planned for raw artifacts, modules, audio, images |
+
+## Phase 1 Surfaces
+
+- 推荐: latest and curated report interpretations.
+- 研报: all published report interpretations with basic filters.
+- 机构: institution list, institution detail, and recent reports.
+- 听单: audio-backed reports.
+- 我的: guest/login state and shallow personal-state entries.
+
+## Key Engineering Principle
+
+The app consumes reviewed display artifacts through the API. Raw NotebookLM artifacts are internal evidence and must not be exposed publicly.
+
+NotebookLM-native content may be cleaned, mapped, reviewed, and assembled deterministically. It must not be silently replaced by local LLM rewriting.
+
+## Repository Documentation
+
+- `README.md`: human entry point.
+- `AGENTS.md`: public agent instructions.
+- `docs/DECISIONS.md`: durable decisions.
+- `docs/DEVELOPMENT_HISTORY.md`: major change history.
+- `report-notebooklm-api/docs/`: backend, data, API, and content pipeline details.
+- `report-notebooklm-app/docs/`: App runbook and API consumption notes.