feat(dashboard): replace emojis with Font Awesome, add theme support, and styled dialogs

This commit implements three major improvements to the dashboard system:

1. **Font Awesome Icons for Tabs**
   - Replace emoji tab icons (📊, 🌍, 🎒) with Font Awesome classes
   - Update defaultLayout.js with fa-solid icon classes
   - Add automatic migration for existing saved dashboards with emoji icons
   - Implement migrateEmojiIcons() to convert old emoji icons on load
   - Update fallback icons throughout the system

2. **Custom Theme Support for Dashboard**
   - Replace all --SmartTheme* variables with --rpg-* variables
   - Ensure custom themes (sci-fi, fantasy, cyberpunk) apply to dashboard
   - Update CSS for tabs, buttons, dropdowns, modals, and widget cards
   - Dashboard now respects extension themes instead of main SillyTavern theme

3. **Styled Confirmation Dialogs**
   - Create confirmDialog.js with showConfirmDialog() and showAlertDialog()
   - Support three variants: danger (red), warning (yellow), info (blue)
   - Add keyboard navigation (Enter/Escape) and accessibility features
   - Replace all native confirm() and alert() calls with styled dialogs
   - Add confirmation dialog modal to dashboardTemplate.html

Files Modified:
- src/systems/dashboard/confirmDialog.js (NEW)
- src/systems/dashboard/dashboardManager.js
- src/systems/dashboard/defaultLayout.js
- src/systems/dashboard/tabManager.js
- src/systems/dashboard/dashboardIntegration.js
- src/systems/dashboard/editModeManager.js
- src/systems/dashboard/widgets/inventoryWidget.js
- src/systems/dashboard/dashboardTemplate.html
- style.css

src/systems/dashboard/defaultLayout.js

@@ -36,7 +36,7 @@ export function generateDefaultDashboard() {
             {
                 id: 'tab-status',
                 name: 'Status',
-                icon: '📊',
+                icon: 'fa-solid fa-user',
                 order: 0,
                 widgets: [
                     // Row 0: User Info (left) + User Mood (top right in 3-col)
@@ -86,7 +86,7 @@ export function generateDefaultDashboard() {
             {
                 id: 'tab-scene',
                 name: 'Scene',
-                icon: '🌍',
+                icon: 'fa-solid fa-map',
                 order: 1,
                 widgets: [
                     // Row 0: Calendar (left) + Weather (right)
@@ -162,7 +162,7 @@ export function generateDefaultDashboard() {
             {
                 id: 'tab-inventory',
                 name: 'Inventory',
-                icon: '🎒',
+                icon: 'fa-solid fa-bag-shopping',
                 order: 2,
                 widgets: [
                     {