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.html

@@ -58,6 +58,15 @@
       <button id="resetDark" class="btn-secondary">Reset Dark Defaults</button>
     </div>
 
+    <div class="section">
+      <h2>Color Presets</h2>
+      <p class="section-hint">Saved color sets. Click to apply to light subreddit badge.</p>
+      <div class="rt-preset-bar">
+        <div id="presetList" class="rt-preset-list"></div>
+        <button id="addPreset" class="rt-preset-add" type="button" title="Save light subreddit colors as preset">+</button>
+      </div>
+    </div>
+
     <div class="section">
       <h2>Per-Subreddit Overrides</h2>
       <p class="section-hint">Set custom subreddit badge colors per mode.</p>