refactor: decompose CSS, unify dark mode, extract shared modules

Structural cleanup based on thermo-nuclear code quality review:
- Extract shared color-picker.css and color-popover.css from badges.css (611→85 lines)
- Extract shared lib/presets.js for preset CRUD used by popup and popover
- Unify dark mode to single applyDarkModeClass on <html>, removing 4 scattered functions
- Fix stale closure in startPostObserver, data-driven reload key check
- Remove dead exports, getHelpers wrapper, duplicated colorToHex
- Replace DOM expando properties with state array in popup.js

Net: -318 lines of duplication, no file over 401 lines.
Co-authored-by: Cursor <cursoragent@cursor.com>

content/main.js

@@ -5,6 +5,7 @@
     var observer = new MutationObserver(function () {
       window.RedditTweaks.loadSettings().then(function (updated) {
         if (updated.darkMode === "auto") {
+          window.RedditTweaks.applyDarkModeClass(updated);
           if (updated.badgeLayout) {
             window.RedditTweaks.badgeTweak.updateColors(updated);
           }
@@ -44,10 +45,10 @@
       }
       if (hasNewPosts) {
         window.RedditTweaks.loadSettings().then(function (updated) {
-          if (settings.badgeLayout) {
+          if (updated.badgeLayout) {
             window.RedditTweaks.badgeTweak.processNewPosts(updated);
           }
-          if (settings.cardLayout) {
+          if (updated.cardLayout) {
             window.RedditTweaks.cardTweak.processNewPosts(updated);
           }
         });
@@ -62,6 +63,8 @@
       var settings = await window.RedditTweaks.loadSettings();
       if (!settings.enabled) return;
 
+      window.RedditTweaks.applyDarkModeClass(settings);
+
       if (settings.badgeLayout) {
         document.documentElement.classList.add("rt-badges-enabled");
         window.RedditTweaks.badgeTweak.apply(settings);
@@ -80,18 +83,19 @@
         startDarkModeObserver(settings);
       }
 
+      var RELOAD_KEYS = ["enabled", "badgeLayout", "fontOverride", "cardLayout"];
+
       browser.storage.onChanged.addListener(function (changes) {
-        if (
-          (changes.enabled && changes.enabled.newValue !== changes.enabled.oldValue) ||
-          (changes.badgeLayout && changes.badgeLayout.newValue !== changes.badgeLayout.oldValue) ||
-          (changes.fontOverride && changes.fontOverride.newValue !== changes.fontOverride.oldValue) ||
-          (changes.cardLayout && changes.cardLayout.newValue !== changes.cardLayout.oldValue)
-        ) {
+        var needsReload = RELOAD_KEYS.some(function (key) {
+          return changes[key] && changes[key].newValue !== changes[key].oldValue;
+        });
+        if (needsReload) {
           location.reload();
           return;
         }
 
         window.RedditTweaks.loadSettings().then(function (updated) {
+          window.RedditTweaks.applyDarkModeClass(updated);
           if (updated.badgeLayout) {
             window.RedditTweaks.badgeTweak.updateColors(updated);
           }