Phase 1: SQLite persistence layer

- Add modernc.org/sqlite (pure Go, no CGO)
- db/ package: trades, orders, config_log tables + CRUD
- Trade persistence: every closed trade saved to SQLite
- Restart recovery: open positions restored from DB
- Automatic migration on startup

go.mod

@@ -1,5 +1,17 @@
 module exchange-monitor
 
-go 1.23.0
+go 1.25.0
 
-require github.com/gorilla/websocket v1.5.3 // indirect
+require (
+	github.com/dustin/go-humanize v1.0.1 // indirect
+	github.com/google/uuid v1.6.0 // indirect
+	github.com/gorilla/websocket v1.5.3 // indirect
+	github.com/mattn/go-isatty v0.0.20 // indirect
+	github.com/ncruces/go-strftime v1.0.0 // indirect
+	github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec // indirect
+	golang.org/x/sys v0.42.0 // indirect
+	modernc.org/libc v1.72.0 // indirect
+	modernc.org/mathutil v1.7.1 // indirect
+	modernc.org/memory v1.11.0 // indirect
+	modernc.org/sqlite v1.50.0 // indirect
+)