storage: add speedtests table + Save/List/Delete + retention

Adds a Store-method API for the RecordSpeedTest RPC (Task 8) and the
retention sweep (Task 14):
  - SaveSpeedTest / ListRecentSpeedTests / DeleteSpeedTestsBefore
  - SpeedTest struct (no json tags; that decision deferred to Task 10)

Schema lives in migrations/002_speedtests.sql to match the existing
embed.FS pattern (rather than inline in Go). The migrate() loop now
iterates every *.sql in lexical order, so future migrations drop in
without code changes. Both files use CREATE ... IF NOT EXISTS so the
existing 001 migration remains idempotent on already-initialised DBs.

CHECK constraints enforce node IN ('fl','pl1') and non-negative metric
values at the DB level. country has no DB CHECK — validation belongs
to the gRPC handler in Task 8.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

internal/storage/speedtests_test.go

@@ -0,0 +1,80 @@
+package storage
+
+import (
+	"context"
+	"path/filepath"
+	"testing"
+	"time"
+)
+
+// newSpeedTestDB mirrors the open pattern from sqlite_test.go since the
+// storage package has no dedicated test-DB helper — every test calls
+// Open(t.TempDir()/...) directly.
+func newSpeedTestDB(t *testing.T) *Store {
+	t.Helper()
+	dir := t.TempDir()
+	st, err := Open(filepath.Join(dir, "test.db"))
+	if err != nil {
+		t.Fatalf("open: %v", err)
+	}
+	t.Cleanup(func() { st.Close() })
+	return st
+}
+
+func TestSpeedTest_SaveAndList(t *testing.T) {
+	db := newSpeedTestDB(t)
+	ctx := context.Background()
+
+	now := time.Now().Unix()
+	id, err := db.SaveSpeedTest(ctx, SpeedTest{
+		Timestamp: now, Node: "fl", Country: "RU",
+		DlMbps: 100.5, UlMbps: 20.1, PingMs: 35.2, JitterMs: 2.4,
+	})
+	if err != nil {
+		t.Fatalf("SaveSpeedTest: %v", err)
+	}
+	if id <= 0 {
+		t.Fatalf("expected positive id, got %d", id)
+	}
+
+	rows, err := db.ListRecentSpeedTests(ctx, 10)
+	if err != nil {
+		t.Fatalf("ListRecentSpeedTests: %v", err)
+	}
+	if len(rows) != 1 {
+		t.Fatalf("expected 1 row, got %d", len(rows))
+	}
+	if rows[0].Country != "RU" || rows[0].Node != "fl" {
+		t.Errorf("row mismatch: %+v", rows[0])
+	}
+}
+
+func TestSpeedTest_RetentionDelete(t *testing.T) {
+	db := newSpeedTestDB(t)
+	ctx := context.Background()
+
+	old := time.Now().Add(-31 * 24 * time.Hour).Unix()
+	fresh := time.Now().Unix()
+
+	for _, ts := range []int64{old, fresh} {
+		if _, err := db.SaveSpeedTest(ctx, SpeedTest{
+			Timestamp: ts, Node: "fl", Country: "RU",
+			DlMbps: 1, UlMbps: 1, PingMs: 1, JitterMs: 1,
+		}); err != nil {
+			t.Fatalf("save: %v", err)
+		}
+	}
+
+	deleted, err := db.DeleteSpeedTestsBefore(ctx, time.Now().Add(-30*24*time.Hour).Unix())
+	if err != nil {
+		t.Fatalf("DeleteSpeedTestsBefore: %v", err)
+	}
+	if deleted != 1 {
+		t.Errorf("expected 1 deleted row, got %d", deleted)
+	}
+
+	rows, _ := db.ListRecentSpeedTests(ctx, 10)
+	if len(rows) != 1 {
+		t.Errorf("expected 1 remaining row, got %d", len(rows))
+	}
+}