feat: add color presets + fix badge hover effect

- Add global color presets: save/apply/delete sets of {bg, border, text}
  colors as reusable presets, shown as mini badges in their own colors.
- Popover: preset badges under preview with + to save, click to apply,
  × on hover to delete.
- Popup: dedicated Color Presets section with same functionality,
  applying to light subreddit badge colors.
- Storage: colorPresets array added to settings defaults.
- Fix badge hover: change brightness(0.9) to brightness(1.1) so hover
  brightens (activates) instead of dimming.

Co-authored-by: Cursor <cursoragent@cursor.com>

popup/popup.css

@@ -210,6 +210,80 @@ fieldset input[type="text"] {
   cursor: pointer;
 }
 
+/* --- Preset badges --- */
+.rt-preset-bar {
+  display: flex;
+  align-items: center;
+  gap: 6px;
+  flex-wrap: wrap;
+  margin-top: 4px;
+}
+
+.rt-preset-list {
+  display: flex;
+  gap: 4px;
+  flex-wrap: wrap;
+}
+
+.rt-preset-badge {
+  display: inline-block;
+  position: relative;
+  border: 1px solid;
+  border-radius: 3px;
+  padding: 2px 6px;
+  font-size: 10px;
+  font-weight: bold;
+  cursor: pointer;
+  line-height: 1.4;
+  user-select: none;
+}
+
+.rt-preset-badge:hover {
+  filter: brightness(1.1);
+}
+
+.rt-preset-delete {
+  display: none;
+  position: absolute;
+  top: -6px;
+  right: -6px;
+  width: 14px;
+  height: 14px;
+  background: #d9534f;
+  color: white;
+  border-radius: 50%;
+  font-size: 10px;
+  line-height: 14px;
+  text-align: center;
+  cursor: pointer;
+}
+
+.rt-preset-badge:hover .rt-preset-delete {
+  display: block;
+}
+
+.rt-preset-add {
+  width: 22px;
+  height: 22px;
+  border: 1px dashed #ccc;
+  border-radius: 3px;
+  background: none;
+  color: #999;
+  font-size: 14px;
+  cursor: pointer;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  flex-shrink: 0;
+  padding: 0;
+}
+
+.rt-preset-add:hover {
+  border-color: #999;
+  color: #666;
+  background: #f5f5f5;
+}
+
 /* --- Color Picker Widget --- */
 .rt-color-picker {
   margin: 8px 0;