feat(inventory): add list/grid view modes with individual item management

Implemented comprehensive individual item management system with toggleable view modes:

- Added item parsing utilities (parseItems/serializeItems) for comma-separated strings
- Implemented list view (full-width rows) and grid view (responsive cards)
- Added view mode toggle buttons per inventory section (onPerson, stored, assets)
- View preferences persist per-section in settings
- Replaced text-based editing with add/remove item controls
- Added inline forms for adding new items (matching existing UX patterns)
- Applied theme accent color (--rpg-highlight) to all outlines and active states
- Updated all tabs (desktop/mobile/inventory subtabs) with theme-consistent styling

Technical improvements:
- Created itemParser.js utility module for item string manipulation
- Enhanced inventory rendering with conditional list/grid HTML generation
- Added switchViewMode handler with settings persistence
- Fixed [object Object] display bug with comprehensive type checking
- All buttons and items now use transparent backgrounds with theme accent borders

src/core/state.js

@@ -61,7 +61,12 @@ export let extensionSettings = {
         cha: 10
     },
     lastDiceRoll: null, // Store last dice roll result
-    collapsedInventoryLocations: [] // Array of collapsed storage location names
+    collapsedInventoryLocations: [], // Array of collapsed storage location names
+    inventoryViewModes: {
+        onPerson: 'list', // 'list' or 'grid' view mode for On Person section
+        stored: 'list',   // 'list' or 'grid' view mode for Stored section
+        assets: 'list'    // 'list' or 'grid' view mode for Assets section
+    }
 };
 
 /**