feat: add SQLite storage for login attempts and sessions

Adds persistent storage using modernc.org/sqlite (pure Go). Login
attempts are deduplicated by (username, password, ip) with counts.
Sessions and session logs are tracked with UUID IDs. Includes embedded
SQL migrations, configurable retention with background pruning, and
an in-memory store for tests.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

cmd/oubliette/main.go

@@ -10,6 +10,7 @@ import (
 
 	"git.t-juice.club/torjus/oubliette/internal/config"
 	"git.t-juice.club/torjus/oubliette/internal/server"
+	"git.t-juice.club/torjus/oubliette/internal/storage"
 )
 
 const Version = "0.1.0"
@@ -46,10 +47,19 @@ func main() {
 	logger := slog.New(handler)
 	slog.SetDefault(logger)
 
+	store, err := storage.NewSQLiteStore(cfg.Storage.DBPath)
+	if err != nil {
+		logger.Error("failed to open database", "err", err)
+		os.Exit(1)
+	}
+	defer store.Close()
+
 	ctx, cancel := signal.NotifyContext(context.Background(), syscall.SIGINT, syscall.SIGTERM)
 	defer cancel()
 
-	srv, err := server.New(*cfg, logger)
+	go storage.RunRetention(ctx, store, cfg.Storage.RetentionDays, cfg.Storage.RetentionIntervalDuration, logger)
+
+	srv, err := server.New(*cfg, store, logger)
 	if err != nil {
 		logger.Error("failed to create server", "err", err)
 		os.Exit(1)