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/AgentsPage.tsx

@@ -310,7 +310,11 @@ export function AgentsPage() {
       header: "hive",
       render: (a) => a.hive ?? "—",
       sortBy: (a) => a.hive ?? "",
-      filterValue: (a) => a.hive ?? "",
+      // "—" (not "") so the missing-hive option in the filter dropdown
+      // reads the same as the cell itself, rather than showing a blank
+      // choice.
+      filterValue: (a) => a.hive ?? "—",
+      filterMode: "select",
     },
     {
       key: "status",
@@ -322,6 +326,7 @@ export function AgentsPage() {
       // now lives in its own "message" column below.
       sortBy: (a) => FRESHNESS[a.freshness].label,
       filterValue: (a) => FRESHNESS[a.freshness].label,
+      filterMode: "select",
       render: (a) => {
         const { tone, label } = FRESHNESS[a.freshness];
         return (
@@ -367,6 +372,7 @@ export function AgentsPage() {
       // callbacks to the page's own state/handlers.
       sortBy: (a) => a.wanted ?? "",
       filterValue: (a) => a.wanted ?? "no declaration",
+      filterMode: "select",
       render: (a) => {
         const err = actionErrors.get(a.name);
         return (

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",
   },
 ];