feat(hamqth): the sent stamp reaches the columns, the filter and bulk edit

HAMLOG.online was wired into all three when it arrived; HamQTH shipped
with only its uploader and its editor row, so the log could not be asked
'which contacts have never gone there' — the question that precedes
every backlog upload — and a log uploaded to HamQTH by hand could not be
marked, leaving OpsLog offering to send every one of those contacts
again. Sent side only, both whitelists, both panels, two hidden-by-
default columns.

internal/qso/qso.go

@@ -995,6 +995,12 @@ var bulkEditableExtras = map[string]string{
 	"hamlog_sent_date": "APP_OPSLOG_HAMLOG_SENT_DATE",
 	"hamlog_rcvd":      "APP_HAMLOG_QSO_CFM",
 	"hamlog_rcvd_date": "APP_OPSLOG_HAMLOG_QSL_DATE",
+	// HamQTH, same story and SENT only — the site publishes no confirmations,
+	// so there is no received side to edit. Bulk-editable for the one case that
+	// matters: a log uploaded to HamQTH by hand, which OpsLog would otherwise
+	// offer to send all over again.
+	"hamqth_sent":      "APP_OPSLOG_HAMQTH_SENT",
+	"hamqth_sent_date": "APP_OPSLOG_HAMQTH_SENT_DATE",
 }
 
 // BulkExtraKey maps a frontend field id to its ADIF key in extras_json, or "".
@@ -1403,6 +1409,10 @@ var filterableExtras = map[string]string{
 	"hamlog_sent_date": "APP_OPSLOG_HAMLOG_SENT_DATE",
 	"hamlog_rcvd":      "APP_HAMLOG_QSO_CFM",
 	"hamlog_rcvd_date": "APP_OPSLOG_HAMLOG_QSL_DATE",
+	// HamQTH — sent only, and filterable for the question that precedes every
+	// backlog upload: "which contacts have never gone there".
+	"hamqth_sent":      "APP_OPSLOG_HAMQTH_SENT",
+	"hamqth_sent_date": "APP_OPSLOG_HAMQTH_SENT_DATE",
 }
 
 // FilterableFields returns the whitelist (for the frontend to build its field