feat(dashboard): add quest widget + fix 4-tab header layout

Quest Widget Integration:
- Created questsWidget.js with Main/Optional quest sub-tabs
- Added dedicated Quests tab (4th tab after Inventory)
- Registered quest widget in dashboardIntegration.js
- Widget features: inline editing, add/remove quests, contenteditable
- Fixed tab switching to use inline re-rendering (not full widget render)

Header Layout Fixes (4+ Tabs):
- Changed header flex-wrap from wrap to nowrap (prevents button wrapping)
- Added icon-only mode for 4+ tabs (disables hover expansion)
- Tab count detection in renderTabs() adds rpg-tabs-icon-only class
- Prevents layout breaking when tabs expand on hover

Technical Details:
- Quest widget follows inventory widget pattern (sub-tabs, per-instance state)
- Split event handlers: attachQuestHandlers (tabs) + attachQuestContentHandlers (buttons)
- Tab switching updates innerHTML inline and re-attaches content handlers
- Default size: 2w × 5h, category: 'scene'

Benefits:
- Quest tracking fully integrated with Dashboard v2 drag/drop
- No header wrapping issues with 4 tabs
- Cleaner icon-only UX when space is constrained
- Horizontal scrolling handles overflow gracefully

src/systems/dashboard/defaultLayout.js

@@ -178,6 +178,26 @@ export function generateDefaultDashboard() {
                         }
                     }
                 ]
+            },
+            // Tab 4: Quests (Full tab for quest system)
+            {
+                id: 'tab-quests',
+                name: 'Quests',
+                icon: 'fa-solid fa-scroll',
+                order: 3,
+                widgets: [
+                    {
+                        id: 'widget-quests',
+                        type: 'quests',
+                        x: 0,
+                        y: 0,
+                        w: 2,
+                        h: 5,
+                        config: {
+                            defaultSubTab: 'main'
+                        }
+                    }
+                ]
             }
         ],