UI polish: update check tooltip date, expand/collapse icons, dialog JS

- NavMenu: show short date in update-check tooltip when last check was not today
- Settings modal: expand/collapse all sections with bi-arrows-expand/collapse icons
- Effective config: add Expand all button (bi-arrows-expand), same icon style as toolbar
- Rename settings-modal.js to dialog.js; add config-option-help.js, JS extension helpers
- Config option help modal and client settings/dialog wiring updates

src/DnsmasqWebUI/Components/Modals/SettingsModal.razor.css

@@ -28,6 +28,15 @@
     padding: 1.25rem;
 }
 
+.settings-expand-collapse-btn {
+    padding: 0.25rem 0.4rem;
+    line-height: 1;
+}
+
+.settings-expand-collapse-btn .bi {
+    font-size: 1rem;
+}
+
 .settings-modal-dialog .modal-footer {
     padding: 1rem 1.25rem;
     border-top: 1px solid rgba(0, 0, 0, 0.125);