fix(regions): rename tab to Regions and soften v1.14 firmware error

Two small follow-ups after initial deployment.

- Rename the Settings tab 'Channels' -> 'Regions' (id now tabSettingsRegions).
  The tab manages the region registry, not channels; the old label was
  confusing. The per-channel picker still lives under Manage Channels as
  before.
- Graceful handling of firmware rejection: CMD_SET_DEFAULT_FLOOD_SCOPE
  (63) and CMD_GET_DEFAULT_FLOOD_SCOPE (64) were introduced in firmware
  v1.15.0; on v1.14.x the device replies with a generic ERR frame and
  our toast showed the unhelpful 'Firmware error: unknown'. Now the
  device_manager translates the empty/timeout reason into a concrete
  message naming the v1.15 requirement, and the api handler appends
  'Your choice is saved locally' so the user knows the local state
  still persists. Same treatment for the delete-default-region clear
  path.

app/static/js/app.js

@@ -2439,7 +2439,7 @@ document.addEventListener('DOMContentLoaded', () => {
     // Initial load so suppress flag is available before user opens Settings
     loadContactsSettings();
 
-    // Channels tab: region registry
+    // Regions tab: region registry
     const addRegionForm = document.getElementById('addRegionForm');
     if (addRegionForm) {
         addRegionForm.addEventListener('submit', (e) => {
@@ -2998,7 +2998,7 @@ function renderRegionPickerList() {
             // Activate the Channels tab after the modal is shown.
             settingsModal.addEventListener('shown.bs.modal', function onceShown() {
                 settingsModal.removeEventListener('shown.bs.modal', onceShown);
-                const btn = document.querySelector('[data-bs-target="#tabSettingsChannels"]');
+                const btn = document.querySelector('[data-bs-target="#tabSettingsRegions"]');
                 if (btn) bootstrap.Tab.getOrCreateInstance(btn).show();
             });
         });