Add core database support and enhance documentation

- Introduced `MYSQL_CORE_DATABASE` in `.env.example` and `settings.py` for core database configuration.
- Added `CoreReadOnlyRepository` for read-only access to the `jinrong_core` database.
- Updated `AGENTS.md`, `README.md`, and various documentation files to reflect new agent onboarding processes and project structure.
- Revised requirements in `requirements.txt` to include `langgraph` and `langchain-core`.
- Enhanced `FLOW.md` with local bootstrap instructions for setting up the core simulation environment.
- Added new scripts for database creation and seeding for the core simulation library.
- Improved overall documentation for clarity on project architecture and memory management.
- Updated `TODO.md` to reflect current development priorities and tasks.

scripts/core/06-seed-nav.sql

@@ -0,0 +1,16 @@
+USE jinrong_core;
+
+-- 最新净值 nav_date = 2026-09-04
+INSERT INTO core_product_nav (product_id, nav, daily_chg_pct, nav_date) VALUES
+('PROD-110022', 1.0300,  0.1500, '2026-09-04'),
+('PROD-110023', 1.0200,  0.1000, '2026-09-04'),
+('PROD-005827', 0.9500, -0.8000, '2026-09-04'),
+('PROD-005828', 1.0200,  0.2000, '2026-09-04'),
+('PROD-161725', 1.0500,  1.2000, '2026-09-04'),
+('PROD-161726', 1.0500,  0.9000, '2026-09-04'),
+('PROD-003095', 0.9500, -1.1000, '2026-09-04'),
+('PROD-510300', 1.0300,  0.3500, '2026-09-04'),
+('PROD-510500', 0.9800, -0.5000, '2026-09-04'),
+('PROD-XYZ999', 0.9000, -2.0000, '2026-09-04'),
+('PROD-000001', 1.0020,  0.0100, '2026-09-04'),
+('PROD-000002', 1.0050,  0.0200, '2026-09-04');