fix: center icons in compact buttons with fixed dimensions and flexbox

Properly centered icons by wrapping text in spans and forcing exact button
dimensions to override base min-width: fit-content style.

Root Cause:
- Base .rpg-inventory-add-btn has min-width: fit-content
- Even with span hidden, button width wasn't constrained
- Icon appeared off-center with extra space to the right

Solution:

1. HTML Structure (inventoryWidget.js, questsWidget.js):
   - Wrapped text in <span class="rpg-btn-label">
   - Pattern: <i class="fa-solid fa-plus"></i><span class="rpg-btn-label"> Add Item</span>
   - Applied to: Add Item, Add Location, Add Asset, Add Quest buttons

2. CSS (style.css):
   - Hide labels: .rpg-inventory-compact .rpg-btn-label { display: none; }
   - Force square dimensions: width: 32px !important (overrides fit-content)
   - Center icon: display: inline-flex; justify-content: center; align-items: center
   - Remove padding: padding: 0 (icon uses full 32px space)

Result: Perfect 32×32px square buttons with centered icons in compact mode,
matching the pattern used for sub-tab buttons throughout the codebase.

Fixes: Icon skewed left in Add Item/Quest buttons at narrow widths

src/systems/dashboard/widgets/inventoryWidget.js

@@ -199,7 +199,7 @@ export function registerInventoryWidget(registry, dependencies) {
                     <div class="rpg-inventory-header-actions">
                         ${renderViewToggle('onPerson', viewMode)}
                         <button class="rpg-inventory-add-btn" data-action="add-item" data-field="onPerson">
-                            <i class="fa-solid fa-plus"></i> Add Item
+                            <i class="fa-solid fa-plus"></i><span class="rpg-btn-label"> Add Item</span>
                         </button>
                     </div>
                 </div>
@@ -302,7 +302,7 @@ export function registerInventoryWidget(registry, dependencies) {
                     <div class="rpg-inventory-header-actions">
                         ${renderViewToggle('stored', viewMode)}
                         <button class="rpg-inventory-add-btn" data-action="add-location">
-                            <i class="fa-solid fa-plus"></i> Add Location
+                            <i class="fa-solid fa-plus"></i><span class="rpg-btn-label"> Add Location</span>
                         </button>
                     </div>
                 </div>
@@ -340,7 +340,7 @@ export function registerInventoryWidget(registry, dependencies) {
                     <div class="rpg-inventory-header-actions">
                         ${renderViewToggle('assets', viewMode)}
                         <button class="rpg-inventory-add-btn" data-action="add-item" data-field="assets">
-                            <i class="fa-solid fa-plus"></i> Add Asset
+                            <i class="fa-solid fa-plus"></i><span class="rpg-btn-label"> Add Asset</span>
                         </button>
                     </div>
                 </div>