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.

scripts/fix_todos_db.py

@@ -0,0 +1,47 @@
+"""Fix: unify todos table schema across project and real DB"""
+import sqlite3
+
+project_db = '/home/hmo/projects/MoFin/data/mofin.db'
+real_db = '/home/hmo/web-dashboard/data/mofin.db'
+
+# Zhiwei's canonical schema (from project db)
+target_schema = """
+    id INTEGER PRIMARY KEY AUTOINCREMENT,
+    title TEXT NOT NULL,
+    description TEXT,
+    status TEXT DEFAULT 'pending',
+    priority TEXT DEFAULT 'medium',
+    source TEXT DEFAULT 'manual',
+    fix_action TEXT,
+    retry_count INTEGER DEFAULT 0,
+    note TEXT,
+    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
+    updated_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
+"""
+
+def ensure_todos(db_path, label):
+    db = sqlite3.connect(db_path)
+    existing = db.execute("SELECT name FROM sqlite_master WHERE name='todos'").fetchone()
+    if not existing:
+        db.execute(f"CREATE TABLE todos ({target_schema})")
+        print(f"{label}: created todos table")
+    else:
+        # Ensure all columns exist
+        existing_cols = {r[1] for r in db.execute("PRAGMA table_info(todos)")}
+        needed = {'title', 'description', 'status', 'priority', 'source', 'fix_action',
+                  'retry_count', 'note', 'created_at', 'updated_at'}
+        missing = needed - existing_cols
+        for col in missing:
+            if col in ('retry_count',):
+                db.execute(f"ALTER TABLE todos ADD COLUMN {col} INTEGER DEFAULT 0")
+            elif col in ('created_at', 'updated_at'):
+                db.execute(f"ALTER TABLE todos ADD COLUMN {col} TIMESTAMP DEFAULT CURRENT_TIMESTAMP")
+            else:
+                db.execute(f"ALTER TABLE todos ADD COLUMN {col} TEXT")
+        print(f"{label}: checked, {len(missing)} missing columns added" if missing else f"{label}: schema OK")
+    db.commit()
+    db.close()
+
+ensure_todos(project_db, "project db")
+ensure_todos(real_db, "real db")
+print("\nDone. Both DBs now have matching todos schema.")