CLI file timestamps reject offsets and discard milliseconds (#20491)

Fixes #20486

## Summary

Try RFC3339/RFC3339Nano and preserve the millisecond remainder when
converting epoch milliseconds.

internal/cli/filesystem/dataset.go

@@ -760,6 +760,8 @@ func parseTime(v interface{}) time.Time {
 			formats := []string{
 				"2006-01-02 15:04:05",
 				"2006-01-02T15:04:05",
+				time.RFC3339Nano,
+				time.RFC3339,
 				"2006-01-02T15:04:05Z",
 				"2006-01-02",
 			}
@@ -774,9 +776,10 @@ func parseTime(v interface{}) time.Time {
 		return time.Time{}
 	}
 
-	// Convert milliseconds to seconds if timestamp is in milliseconds (13 digits)
+	// Convert milliseconds to seconds if timestamp is in milliseconds (13 digits),
+	// preserving the sub-second remainder.
 	if ts > 1e12 {
-		ts = ts / 1000
+		return time.Unix(ts/1000, (ts%1000)*int64(time.Millisecond))
 	}
 
 	return time.Unix(ts, 0)

internal/cli/filesystem/r3_regression_test.go

@@ -0,0 +1,31 @@
+package filesystem
+
+import (
+	"encoding/json"
+	"testing"
+	"time"
+)
+
+func TestParseTimeRFC3339WithOffset(t *testing.T) {
+	got := parseTime("2026-09-30T15:04:05+05:30")
+	if got.IsZero() {
+		t.Fatal("RFC3339 timestamp with zone offset must parse, got zero time")
+	}
+	want, _ := time.Parse(time.RFC3339, "2026-09-30T15:04:05+05:30")
+	if !got.Equal(want) {
+		t.Fatalf("got %v, want %v", got, want)
+	}
+}
+
+func TestParseTimeMillisecondsRemainder(t *testing.T) {
+	var record map[string]interface{}
+	if err := json.Unmarshal([]byte(`{"created_at":1727700000123}`), &record); err != nil {
+		t.Fatal(err)
+	}
+	for _, input := range []interface{}{int64(1727700000123), record["created_at"]} {
+		got := parseTime(input)
+		if got.UnixMilli() != 1727700000123 {
+			t.Fatalf("millisecond remainder lost for %T: got %d", input, got.UnixMilli())
+		}
+	}
+}