feat(cluster): a SOTA column, and a spot click that credits the summit

The SOTA feeds put the summit in the spot's own text, so there is nothing to
poll: a regex on the comment gives the reference, and clicking the spot writes
SOTA@<ref> into the award references the way a park already wrote POTA@<ref>.

The regex is narrow on purpose — association/region-NNN, anchored — because
POTA (US-4475), WWFF (DLFF-0001) and portable callsigns (DL/SP9DPM/P) share
that field and none of them is a summit. Pinned by a table test.

Off by default: the reference is only there on the summit feeds, and an empty
column for every operator who does not chase them is worse than a checkbox.

internal/cluster/cluster_test.go

@@ -110,7 +110,7 @@ func TestParseShowDX(t *testing.T) {
 // chatter turned into fake spots would be worse than no parser at all.
 func TestParseShowDXRejectsNoise(t *testing.T) {
 	noise := []string{
-		"DX de F5ABC:     14195.0  EA8DHH       CQ DX                 1234Z",  // the broadcast form: spotRE owns it
+		"DX de F5ABC:     14195.0  EA8DHH       CQ DX                 1234Z", // the broadcast form: spotRE owns it
 		"Hello and welcome to the DXSpider cluster",
 		"WWV de VE7CC <18Z> : SFI=110, A=16, K=2",
 		"F4BPO de GB7DXC 12-Jul-2026 2130Z dxspider >",