fix(theme): make checkboxes and loading spinner follow the theme accent

Native checkboxes in settings (managed types, base-model skip list) and the
folder-root delete modal had no color declaration, so checked state used the
browser default blue; the loading spinner used hardcoded #3498db/#f3f3f3.
Give the checkboxes accent-color: var(--lora-accent) and derive the spinner
track/arc from the accent token so all themes and presets stay consistent.

static/css/components/loading.css

@@ -22,8 +22,8 @@
 }
 
 .loading-spinner {
-    border: 4px solid #f3f3f3;
-    border-top: 4px solid #3498db;
+    border: 4px solid oklch(from var(--lora-accent) l c h / 0.2);
+    border-top: 4px solid var(--lora-accent);
     border-radius: 50%;
     width: 40px;
     height: 40px;

static/css/components/modal/delete-modal.css

@@ -149,6 +149,7 @@
 .folder-root-option input[type="checkbox"] {
     margin-top: 2px;
     flex: 0 0 auto;
+    accent-color: var(--lora-accent);
 }
 
 /* Path over status, so a row keeps its height when the verdict replaces

static/css/components/modal/settings-modal.css

@@ -607,6 +607,7 @@
 
 .base-model-skip-option input {
     margin: 0;
+    accent-color: var(--lora-accent);
 }
 
 .base-model-skip-option span {
@@ -1849,6 +1850,7 @@ input:checked + .toggle-slider:before {
 
 .other-subtype-checkbox input[type="checkbox"] {
     cursor: pointer;
+    accent-color: var(--lora-accent);
 }
 
 .other-subtype-toggles.is-disabled {