fix: robust SQLite timestamp parsing for hub dashboard

Replace hardcoded time.Parse with parseSQLiteTime() that handles multiple
formats returned by modernc.org/sqlite, fixing hub showing DOWN status
and 00:00:00 timestamps in report history.

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

hub/internal/store/store.go

@@ -148,7 +148,7 @@ func (s *Store) GetCustomers() ([]CustomerSummary, error) {
 			return nil, err
 		}
 
-		c.ReceivedAt, _ = time.Parse("2006-01-02 15:04:05", receivedAt)
+		c.ReceivedAt = parseSQLiteTime(receivedAt)
 		c.TimeSinceReport = time.Since(c.ReceivedAt)
 
 		if backupSnapshot.Valid {
@@ -199,7 +199,7 @@ func (s *Store) GetCustomer(customerID string) (*CustomerSummary, error) {
 		return nil, err
 	}
 
-	c.ReceivedAt, _ = time.Parse("2006-01-02 15:04:05", receivedAt)
+	c.ReceivedAt = parseSQLiteTime(receivedAt)
 	c.TimeSinceReport = time.Since(c.ReceivedAt)
 
 	if backupSnapshot.Valid {
@@ -250,7 +250,7 @@ func (s *Store) GetCustomerHistory(customerID string, since time.Duration) ([]Cu
 			return nil, err
 		}
 
-		c.ReceivedAt, _ = time.Parse("2006-01-02 15:04:05", receivedAt)
+		c.ReceivedAt = parseSQLiteTime(receivedAt)
 		c.TimeSinceReport = time.Since(c.ReceivedAt)
 
 		if backupSnapshot.Valid {
@@ -280,6 +280,28 @@ func (s *Store) Close() error {
 	return s.db.Close()
 }
 
+// parseSQLiteTime tries multiple formats that modernc.org/sqlite may return.
+func parseSQLiteTime(s string) time.Time {
+	formats := []string{
+		"2006-01-02 15:04:05",          // SQLite datetime('now')
+		"2006-01-02T15:04:05Z",         // RFC3339 without fractional
+		time.RFC3339,                    // 2006-01-02T15:04:05Z07:00
+		time.RFC3339Nano,               // with fractional seconds
+		"2006-01-02 15:04:05+00:00",    // with explicit UTC offset
+		"2006-01-02 15:04:05.999999999", // with fractional, no TZ
+	}
+	for _, f := range formats {
+		if t, err := time.Parse(f, s); err == nil {
+			return t
+		}
+	}
+	// Last resort: if string is non-empty, log it for debugging
+	if s != "" {
+		log.Printf("[WARN] Could not parse timestamp: %q", s)
+	}
+	return time.Time{} // zero time
+}
+
 func parseDiskSummary(reportJSON string) string {
 	var report struct {
 		Storage []struct {