cmd/speedtest-sync: fail-fast on bad timestamps + minor cleanups

- Skip rows with null/malformed timestamps instead of silently
  re-stamping with time.Now() (data corruption hidden behind a
  fallback). Drops the time import.
- Replace ad-hoc parentDir() with stdlib filepath.Dir().
- Add t.Fatal error checks to TestExtractRows_SkipsBadExtra
  (CREATE TABLE / INSERT) and switch sql.Open to checked form.
- New TestExtractRows_SkipsBadTimestamp covers the null-ts path.

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

cmd/speedtest-sync/sync_test.go

@@ -54,15 +54,22 @@ func TestExtractRows_FiltersExtraJSON(t *testing.T) {
 func TestExtractRows_SkipsBadExtra(t *testing.T) {
 	dir := t.TempDir()
 	dbPath := filepath.Join(dir, "test.db")
-	db, _ := sql.Open("sqlite", dbPath)
+	db, err := sql.Open("sqlite", dbPath)
+	if err != nil {
+		t.Fatal(err)
+	}
 	defer db.Close()
 
-	db.Exec(`CREATE TABLE speedtest_users (
+	if _, err := db.Exec(`CREATE TABLE speedtest_users (
 		id INTEGER PRIMARY KEY AUTOINCREMENT,
 		timestamp DATETIME, ip TEXT, ispinfo TEXT, extra TEXT,
-		ua TEXT, lang TEXT, dl REAL, ul REAL, ping REAL, jitter REAL, log TEXT)`)
-	db.Exec(`INSERT INTO speedtest_users(timestamp, extra, dl, ul, ping, jitter)
-             VALUES(datetime('now'), 'not-json', 1, 1, 1, 1)`)
+		ua TEXT, lang TEXT, dl REAL, ul REAL, ping REAL, jitter REAL, log TEXT)`); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := db.Exec(`INSERT INTO speedtest_users(timestamp, extra, dl, ul, ping, jitter)
+             VALUES(datetime('now'), 'not-json', 1, 1, 1, 1)`); err != nil {
+		t.Fatal(err)
+	}
 
 	rows, err := extractRows(context.Background(), db, 0)
 	if err != nil {
@@ -72,3 +79,35 @@ func TestExtractRows_SkipsBadExtra(t *testing.T) {
 		t.Errorf("expected 0 rows (bad extra skipped), got %d", len(rows))
 	}
 }
+
+func TestExtractRows_SkipsBadTimestamp(t *testing.T) {
+	dir := t.TempDir()
+	dbPath := filepath.Join(dir, "test.db")
+	db, err := sql.Open("sqlite", dbPath)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer db.Close()
+
+	if _, err := db.Exec(`CREATE TABLE speedtest_users (
+		id INTEGER PRIMARY KEY AUTOINCREMENT,
+		timestamp DATETIME, ip TEXT, ispinfo TEXT, extra TEXT,
+		ua TEXT, lang TEXT, dl REAL, ul REAL, ping REAL, jitter REAL, log TEXT)`); err != nil {
+		t.Fatal(err)
+	}
+
+	extra, _ := json.Marshal(map[string]string{"node": "fl", "country": "RU"})
+	// NULL timestamp
+	if _, err := db.Exec(`INSERT INTO speedtest_users(timestamp, extra, dl, ul, ping, jitter)
+		VALUES(NULL, ?, 1, 1, 1, 1)`, string(extra)); err != nil {
+		t.Fatal(err)
+	}
+
+	rows, err := extractRows(context.Background(), db, 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(rows) != 0 {
+		t.Errorf("expected 0 rows (null timestamp skipped), got %d", len(rows))
+	}
+}