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/sotaref.go

@@ -0,0 +1,21 @@
+package cluster
+
+import "regexp"
+
+// sotaRefRe matches a SOTA summit reference inside a spot comment.
+//
+// The shape is association/region-NNN — "W9/WI-001", "DM/BM-063", "VK3/VC-014",
+// "F/AM-123" — and the association may carry digits. Anchored on both sides so
+// a callsign like DL/SP9DPM/P can never be read as one, and deliberately
+// narrower than "anything with a slash and a dash": POTA (US-4475) and WWFF
+// (DLFF-0001) refs share the comment field and must not be caught here.
+var sotaRefRe = regexp.MustCompile(`\b([A-Z0-9]{1,4}(?:/[A-Z0-9]{1,4})?/[A-Z]{2}-[0-9]{3})\b`)
+
+// SOTARefFrom returns the first SOTA reference in a spot comment, or "".
+func SOTARefFrom(comment string) string {
+	m := sotaRefRe.FindStringSubmatch(comment)
+	if m == nil {
+		return ""
+	}
+	return m[1]
+}