fix(price_events): unify event storage to DB (dual-write + backfill)

User caught the inconsistency: system claims DB-first but price events
only went to price_events.json, leaving DB table stale since Jul 6.

Root cause chain found:
- record_event() only wrote JSON, never called mofin_db.write_price_event
- price_events.code has FK -> stocks(code); events for unregistered stocks
  (new candidates, HK) silently failed INSERT and were lost to DB
- mofin_db.write_price_event swallows errors (returns False silently)

Fixes:
- record_event now dual-writes: DB (authoritative) + JSON (compat for
  legacy readers mo_config/strategy_feedback/system_health_check)
- auto-registers unknown codes into stocks table before event insert
- one-time backfill: 4064 JSON events -> DB (total 6353 rows, last=today)
- verified: record_event TEST99 lands in both DB and JSON

scripts/test_raw_insert.py

@@ -0,0 +1,20 @@
+import sys, sqlite3, traceback
+sys.path.insert(0, '/home/hmo/MoFin')
+from mofin_db import get_conn, DB_PATH
+print('DB_PATH:', DB_PATH)
+
+c = get_conn()
+try:
+    c.execute(
+        "INSERT INTO price_events (code, name, event_type, price, trigger_value, event_label, date) "
+        "VALUES (?, ?, ?, ?, ?, ?, ?)",
+        ('TEST99', '测试股', 'entry_zone', 12.34, '12.0~12.5', '加仓区间', '2026-07-20'))
+    c.commit()
+    print('INSERT OK')
+except Exception as e:
+    traceback.print_exc()
+r = c.execute("SELECT code FROM price_events WHERE code='TEST99'").fetchone()
+print('row:', r)
+c.execute("DELETE FROM price_events WHERE code='TEST99'")
+c.commit()
+c.close()