fix(#732): apply pre-PR review to the preset catalog

RadioPreset.frequencyHz returned kHz; renamed frequencyKHz (the unit
CMD_SET_RADIO_PARAMS carries). The picker is disabled while a refresh
runs, so a pick can't vanish when the refreshed list lands, and the
selected-item builder uses an id-to-title map.

Epic: #726
Agent: MagentaHawk (session 5a8922d6)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

lib/models/radio_preset.dart

@@ -54,7 +54,8 @@ class RadioPreset {
   /// A client-repeat (off-grid) frequency rather than a regional preset.
   final bool offGrid;
 
-  int get frequencyHz => (frequencyMHz * 1000).round();
+  /// Frequency in kHz, the unit CMD_SET_RADIO_PARAMS carries.
+  int get frequencyKHz => (frequencyMHz * 1000).round();
 
   /// The firmware's path hash mode for [pathHashBytes], or null to leave it.
   ///

lib/screens/settings_screen.dart

@@ -2152,7 +2152,8 @@ class _RadioSettingsFormState extends State<_RadioSettingsForm> {
     _RadioSettingsSnapshot snapshot, {
     int? frequencyHz,
   }) {
-    return (frequencyHz ?? preset.frequencyHz) == snapshot.frequencyHz &&
+    // _RadioSettingsSnapshot.frequencyHz is also kHz, despite its name.
+    return (frequencyHz ?? preset.frequencyKHz) == snapshot.frequencyHz &&
         preset.bandwidth == snapshot.bandwidth &&
         preset.spreadingFactor == snapshot.spreadingFactor &&
         preset.codingRate == snapshot.codingRate &&

lib/widgets/radio_preset_picker.dart

@@ -36,6 +36,7 @@ class RadioPresetPicker extends StatelessWidget {
     final l10n = context.l10n;
     final theme = Theme.of(context);
     final selected = _byId(selectedId)?.id;
+    final titlesById = {for (final p in presets) p.id: p.title};
     final items = <DropdownMenuItem<String>>[];
     String? region;
     for (final preset in presets) {
@@ -99,16 +100,20 @@ class RadioPresetPicker extends StatelessWidget {
               Align(
                 alignment: AlignmentDirectional.centerStart,
                 child: Text(
-                  _byId(item.value)?.title ?? '',
+                  titlesById[item.value] ?? '',
                   overflow: TextOverflow.ellipsis,
                 ),
               ),
           ],
           items: items,
-          onChanged: (id) {
-            final preset = _byId(id);
-            if (preset != null) onSelected(preset);
-          },
+          // Disabled while a refresh runs, so a pick can't vanish when the
+          // refreshed list lands.
+          onChanged: service.refreshing
+              ? null
+              : (id) {
+                  final preset = _byId(id);
+                  if (preset != null) onSelected(preset);
+                },
         ),
         _PresetStatus(service: service),
       ],

test/connector/preset_apply_frames_test.dart

@@ -36,14 +36,14 @@ void main() {
     final philly = named('USA - Philly Mesh');
     // The form sends MHz * 1000, i.e. kHz; stock stores freq / 1000.0 as MHz.
     final frame = buildSetRadioParamsFrame(
-      philly.frequencyHz,
+      philly.frequencyKHz,
       philly.bandwidth.hz,
       philly.spreadingFactor.value,
       philly.codingRate.value,
     );
     expect(frame, [cmdSetRadioParams, ...le32(919500), ...le32(500000), 10, 5]);
     // Inside stock's accepted ranges (150000-2500000 kHz, BW <= 500000 Hz).
-    expect(philly.frequencyHz, inInclusiveRange(150000, 2500000));
+    expect(philly.frequencyKHz, inInclusiveRange(150000, 2500000));
     expect(philly.bandwidth.hz, lessThanOrEqualTo(500000));
   });
 

test/models/radio_preset_test.dart

@@ -60,7 +60,7 @@ void main() {
       final socal = r.presets[0];
       expect(socal.id, 'meshcore:USA - Southern California');
       expect(socal.region, 'USA');
-      expect(socal.frequencyHz, 927875);
+      expect(socal.frequencyKHz, 927875);
       expect(socal.bandwidth, LoRaBandwidth.bw62_5);
       expect(socal.spreadingFactor, LoRaSpreadingFactor.sf7);
       expect(socal.codingRate, LoRaCodingRate.cr4_5);

test/services/radio_preset_service_test.dart

@@ -283,7 +283,7 @@ void main() {
       final merged = mergeRadioPresets(upstream.presets, overlay.presets);
       expect(merged.length, 59);
       final philly = merged.firstWhere((p) => p.title == 'USA - Philly Mesh');
-      expect(philly.frequencyHz, 919500);
+      expect(philly.frequencyKHz, 919500);
       expect(philly.bandwidth, LoRaBandwidth.bw500);
       expect(philly.pathHashMode, 1);
       final euNarrow = merged.firstWhere((p) => p.title == 'EU/UK (Narrow)');