Fixes #5: Refactor code quality - Part 1

- Split index.js from 1,567 lines to 456 lines (73% reduction)
  - Extracted settings event listeners to src/systems/ui/settingsListeners.js
  - Extracted settings panel to src/core/settingsPanel.js
  - Simplified initUI() and main initialization block

- Modularized style.css into 28 logical CSS modules in src/styles/
  - Added build script (npm run build:css) to concatenate modules
  - Modules: panel, components, user-stats, info-box, thoughts, settings,
    themes, modals, mobile, inventory, quests, equipment, encounters,
    weather, music-player, FAB widgets, strip widgets, etc.

- Updated package.json with build:css script and type: module

No functional changes - pure refactoring for maintainability.

package.json

@@ -1,9 +1,11 @@
 {
-  "name": "rpg-complanion-sillytavern",
+  "name": "rpg-companion-sillytavern",
   "version": "3.7.4",
-  "description": "",
+  "description": "RPG Companion extension for SillyTavern",
   "main": "index.js",
+  "type": "module",
   "scripts": {
+    "build:css": "node scripts/build-css.js",
     "validate_locale": "node src/i18n/validator.js --watch",
     "validate_locale_once": "node src/i18n/validator.js"
   },