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/price_history.json

@@ -27,6 +27,12 @@
       "high": 1215.52,
       "low": 1185.0,
       "close": 1194.45
+    },
+    {
+      "date": "2026-07-06",
+      "high": 1215.0,
+      "low": 1180.0,
+      "close": 1203.23
     }
   ],
   "02202": [
@@ -63,6 +69,12 @@
       "high": 50.2,
       "low": 48.31,
       "close": 49.09
+    },
+    {
+      "date": "2026-07-06",
+      "high": 49.96,
+      "low": 48.81,
+      "close": 49.38
     }
   ],
   "02359": [
@@ -119,6 +131,12 @@
       "high": 502.0,
       "low": 444.55,
       "close": 480.32
+    },
+    {
+      "date": "2026-07-06",
+      "high": 499.0,
+      "low": 448.0,
+      "close": 476.72
     }
   ],
   "06160": [
@@ -155,6 +173,12 @@
       "high": 687.04,
       "low": 633.01,
       "close": 643.81
+    },
+    {
+      "date": "2026-07-06",
+      "high": 649.88,
+      "low": 615.0,
+      "close": 649.01
     }
   ],
   "09868": [
@@ -197,6 +221,12 @@
       "high": 757.88,
       "low": 713.0,
       "close": 738.38
+    },
+    {
+      "date": "2026-07-06",
+      "high": 745.0,
+      "low": 690.11,
+      "close": 743.0
     }
   ],
   "300124": [
@@ -211,6 +241,12 @@
       "high": 74.63,
       "low": 67.31,
       "close": 72.15
+    },
+    {
+      "date": "2026-07-06",
+      "high": 71.94,
+      "low": 68.6,
+      "close": 69.55
     }
   ],
   "000657": [
@@ -225,6 +261,12 @@
       "high": 101.5,
       "low": 87.88,
       "close": 89.63
+    },
+    {
+      "date": "2026-07-06",
+      "high": 90.58,
+      "low": 80.46,
+      "close": 81.83
     }
   ],
   "000711": [
@@ -239,6 +281,12 @@
       "high": 5.26,
       "low": 4.87,
       "close": 5.26
+    },
+    {
+      "date": "2026-07-06",
+      "high": 5.65,
+      "low": 5.0,
+      "close": 5.29
     }
   ],
   "001309": [
@@ -253,6 +301,12 @@
       "high": 892.1,
       "low": 795.0,
       "close": 881.91
+    },
+    {
+      "date": "2026-07-06",
+      "high": 918.98,
+      "low": 860.0,
+      "close": 916.6
     }
   ],
   "002594": [
@@ -267,6 +321,12 @@
       "high": 88.88,
       "low": 81.9,
       "close": 88.47
+    },
+    {
+      "date": "2026-07-06",
+      "high": 88.95,
+      "low": 86.61,
+      "close": 87.68
     }
   ],
   "00700": [
@@ -335,6 +395,12 @@
       "high": 646.85,
       "low": 574.1,
       "close": 618.02
+    },
+    {
+      "date": "2026-07-06",
+      "high": 710.0,
+      "low": 659.16,
+      "close": 695.26
     }
   ]
 }