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>

lib/presets.js

@@ -0,0 +1,57 @@
+(function () {
+  "use strict";
+
+  function renderPresets(container, presets, onApply, onDelete) {
+    container.innerHTML = "";
+    for (var i = 0; i < presets.length; i++) {
+      (function (index) {
+        var p = presets[index];
+        var badge = document.createElement("span");
+        badge.className = "rt-preset-badge";
+        badge.style.background = p.bg;
+        badge.style.borderColor = p.border;
+        badge.style.color = p.text;
+        badge.textContent = "Aa";
+        badge.title = "Click to apply";
+        badge.addEventListener("click", function () {
+          onApply(p);
+        });
+
+        var del = document.createElement("span");
+        del.className = "rt-preset-delete";
+        del.textContent = "\u00d7";
+        del.addEventListener("click", function (e) {
+          e.stopPropagation();
+          onDelete(index);
+        });
+        badge.appendChild(del);
+        container.appendChild(badge);
+      })(i);
+    }
+  }
+
+  async function savePreset(preset, onDone) {
+    var settings = await window.RedditTweaks.loadSettings();
+    var presets = settings.colorPresets || [];
+    presets.push(preset);
+    settings.colorPresets = presets;
+    await window.RedditTweaks.saveSettings(settings);
+    onDone(presets);
+  }
+
+  async function deletePreset(index, onDone) {
+    var settings = await window.RedditTweaks.loadSettings();
+    var presets = settings.colorPresets || [];
+    presets.splice(index, 1);
+    settings.colorPresets = presets;
+    await window.RedditTweaks.saveSettings(settings);
+    onDone(presets);
+  }
+
+  window.RedditTweaks = window.RedditTweaks || {};
+  window.RedditTweaks.presets = {
+    render: renderPresets,
+    save: savePreset,
+    delete: deletePreset,
+  };
+})();

lib/settings.js

@@ -76,6 +76,14 @@
     return isDarkMode(settings) ? "dark" : "light";
   }
 
+  function applyDarkModeClass(settings) {
+    if (isDarkMode(settings)) {
+      document.documentElement.classList.add("rt-dark");
+    } else {
+      document.documentElement.classList.remove("rt-dark");
+    }
+  }
+
   window.RedditTweaks = window.RedditTweaks || {};
   window.RedditTweaks.DEFAULTS = DEFAULTS;
   window.RedditTweaks.loadSettings = loadSettings;
@@ -83,4 +91,5 @@
   window.RedditTweaks.resetSettings = resetSettings;
   window.RedditTweaks.isDarkMode = isDarkMode;
   window.RedditTweaks.getColorPrefix = getColorPrefix;
+  window.RedditTweaks.applyDarkModeClass = applyDarkModeClass;
 })();