feat: DB-first architecture with lock-safe writes

- price_monitor: writes live prices to both JSON and mofin.db (holdings + live_prices + portfolio_summary)
- mofin_db: added execute_with_retry/commit_with_retry with exponential backoff on 'database is locked'
- mofin_db: increased timeout 5s->15s, added PRAGMA busy_timeout=15000
- price_monitor retry loop: fixed break-before-if-ok bug (was not retrying on write failure)
- DB connection: WAL mode + retry decorator for all write operations
- cash sync: preserves DB authoritative cash (JSON cash not pushed to DB)

This is the DB-first version. JSON writes remain for dashboard compatibility.
Next step: remove JSON writes entirely for full DB-only architecture.

data/stocks/01478.json

@@ -456,6 +456,16 @@
       "content": "③ 丘钛科技(01478) 距止损6.48仅+7.3%！仓位7.97%",
       "report_id": "cron_d42f2ce3b479_2026-07-03_20-03-44"
     },
+    {
+      "time": "2026-07-06T08:55:01.761812",
+      "content": "2. **收紧输出质量** — 使用\"关注/观望/留意\"时须紧随具体价格、止损位和触发条件。满 3 次模糊表述自动标记为低质量输出。对 01478 和 688795 做一次明确的持仓策略复核：继续持有",
+      "report_id": "cron_e02b8bde74f8_2026-07-05_22-05-42"
+    },
+    {
+      "time": "2026-07-06T08:55:01.761812",
+      "content": "| **丘钛科技(01478)** | 7.97% 第三大仓位，成本 ¥13.47 远超止盈 ¥7.59（浮亏约 -43%），150 次提及却无追踪结论。无论继续持有还是止损，需 Dad 明确决策 |",
+      "report_id": "cron_e02b8bde74f8_2026-07-05_22-05-42"
+    },
     {
       "time": "2026-06-01T10:25:54.503460",
       "content": "丘钛科技(01478) 仓位8.58% +4.10%→ 持有，走势健康",