Add customizable RPG attributes and fix character stats editing

Features:
- Made RPG attributes (STR/DEX/CON/INT/WIS/CHA) fully customizable
- Added enable/disable toggle for entire RPG Attributes section
- Users can add/remove/rename/toggle individual attributes
- Custom attribute names now appear in AI prompts for dice rolls
- Added proper CSS styling for attribute editor fields

Bug Fixes:
- Fixed character stat editing showing 0% on blur but saving correctly
- Character stats now create Stats line if missing from AI response
- Separated stat name from editable percentage value
- Added value sanitization (removes %, validates 0-100 range)
- Stats line now inserts before Thoughts line when created

Technical:
- Added buildAttributesString() helper in promptBuilder.js
- Updated generateTrackerInstructions and generateContextualSummary
- Restructured character stat HTML to prevent nested contenteditable
- Enhanced updateCharacterField to handle missing Stats lines
- Removed legacy default preset/regex import code

src/core/persistence.js

@@ -365,6 +365,7 @@ function migrateToTrackerConfig() {
         extensionSettings.trackerConfig = {
             userStats: {
                 customStats: [],
+                showRPGAttributes: true,
                 rpgAttributes: [
                     { id: 'str', name: 'STR', enabled: true },
                     { id: 'dex', name: 'DEX', enabled: true },
@@ -457,6 +458,11 @@ function migrateToTrackerConfig() {
         ];
     }
 
+    // Ensure showRPGAttributes exists (defaults to true)
+    if (extensionSettings.trackerConfig.userStats.showRPGAttributes === undefined) {
+        extensionSettings.trackerConfig.userStats.showRPGAttributes = true;
+    }
+
     // Ensure all rpgAttributes have corresponding values in classicStats
     if (extensionSettings.classicStats) {
         for (const attr of extensionSettings.trackerConfig.userStats.rpgAttributes) {