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.

strategy_lifecycle.py

@@ -698,9 +698,8 @@ def compute_sector_adjustment(code, market_ctx, stock_sector_map):
 def load_macro_context():
     """读取宏观上下文，返回 (bias, desc)，优先 DB，回退 JSON"""
     try:
-        import sqlite3
-        from pathlib import Path
-        conn = sqlite3.connect(str(Path(__file__).parent.parent / "data" / "mofin.db"))
+        from mofin_db import get_conn
+        conn = get_conn()
         row = conn.execute(
             "SELECT indices, structure FROM macro_context_log "
             "WHERE has_valid_data=1 ORDER BY created_at DESC LIMIT 1"
@@ -740,9 +739,8 @@ def batch_fetch_prices(codes):
     
     # 主通道：从 DB 读取（price_monitor 唯一价格入口）
     try:
-        import sqlite3
-        db = sqlite3.connect('/home/hmo/web-dashboard/data/mofin.db')
-        db.row_factory = sqlite3.Row
+        from mofin_db import get_conn
+        db = get_conn()
         for raw_code in codes:
             raw_code = str(raw_code).split('_')[0]
             if not raw_code: continue
@@ -842,9 +840,8 @@ def get_price_tencent(code):
     
     # 主通道: DB
     try:
-        import sqlite3
-        db = sqlite3.connect('/home/hmo/web-dashboard/data/mofin.db')
-        db.row_factory = sqlite3.Row
+        from mofin_db import get_conn
+        db = get_conn()
         row = db.execute("SELECT price FROM holdings WHERE code=? AND is_active=1", (raw_code,)).fetchone()
         if not row:
             row = db.execute("SELECT price FROM holding_strategies WHERE code=? AND status='active' ORDER BY updated_at DESC LIMIT 1", (raw_code,)).fetchone()