swarm-ui: bounded-domain table filters become dropdowns

Table columns whose value only ever comes from a small closed set
(freshness, wanted, hive) get a <select> in their filter-row cell
instead of a free-text input, populated from the distinct values
present in the currently-loaded rows plus an "any" option, matched by
exact equality instead of substring. Free-text columns (name, the
agent's own status message, config PR, hive domain) are unchanged.

frontend/packages/swarm-ui/src/pages/HivesPage.tsx

@@ -92,6 +92,7 @@ const COLUMNS: TableColumn<HiveStatus>[] = [
     },
     sortBy: (h) => FRESHNESS[h.freshness].label,
     filterValue: (h) => FRESHNESS[h.freshness].label,
+    filterMode: "select",
   },
 ];