feat: implement Skills widget with level progression and categories

Add comprehensive Skills widget to dashboard system with category organization,
XP tracking, level progression, and multiple view modes.

Widget Features:
- Three sub-tabs: All Skills, By Category, Quick View
- Level-up and level-down buttons for manual progression
- XP progress bars with visual feedback
- Search and filter functionality
- Category collapse/expand in By Category view
- Editable skill names and categories
- Delete skills and categories
- Add new skills and categories
- Configurable max level and XP display

UI Improvements:
- Scrollable content area for large skill lists
- Responsive card layout
- Shortened tab labels for compact display ("All", "Quick" vs "All Skills", "Quick View")
- Proper flex layout for skill names (no longer truncated)
- Level badges and action buttons

Technical Implementation:
- Event handler deduplication to prevent exponential level-up bug
- Flag-based handler attachment: container.dataset.handlersAttached
- Nested flex containers for proper space distribution
- Scrollable views wrapper matching Inventory/Quests pattern

Dashboard Integration:
- Added Skills tab to defaultLayout.js (tab 5)
  - Icon: fa-solid fa-book (fixed invalid fa-book-sparkles)
  - Dimensions: 3x7 grid cells
  - Default config: All Skills tab, show XP, show categories
- Auto-arrange support in dashboardManager.js
  - Skills category group with priority order 6
  - Auto-creates Skills tab when skills widgets detected
- Widget registration in dashboardIntegration.js

Widget Files:
- src/systems/dashboard/widgets/userSkillsWidget.js (new)
  - Full widget implementation with all sub-tabs and features
  - State management with Map-based storage
  - Category-based and flat views
  - Search/filter/sort functionality

Styling:
- style.css: Added skills widget styles
  - Skill cards, headers, action buttons
  - Level-down button with accent color
  - XP progress bars
  - Category sections

Fixes from iteration:
1. Invalid FontAwesome icon (fa-book-sparkles → fa-book)
2. Tab labels too wide (shortened to single words)
3. Skill names truncated (fixed with proper flex structure)
4. Widget height incorrect (adjusted to h:7)
5. Level-up exponential bug (duplicate handlers, added flag guard)
6. No level-down button (added with minimum level 1)
7. No scrollbar on long lists (added .rpg-skills-views wrapper)

Category: skills
Integration: Fully integrated with dashboard v2.0 system
Tested: Layout, interactions, scrolling, level progression

Refs: AI tracker integration (separate commit)

src/systems/dashboard/defaultLayout.js

@@ -167,6 +167,29 @@ export function generateDefaultDashboard() {
                         }
                     }
                 ]
+            },
+            // Tab 5: Skills (Full tab for skills system)
+            {
+                id: 'tab-skills',
+                name: 'Skills',
+                icon: 'fa-solid fa-book',
+                order: 4,
+                widgets: [
+                    {
+                        id: 'widget-userskills',
+                        type: 'userSkills',
+                        x: 0,
+                        y: 0,
+                        w: 3,
+                        h: 7,
+                        config: {
+                            defaultSubTab: 'all',
+                            showXP: true,
+                            showCategories: true,
+                            maxLevel: 10
+                        }
+                    }
+                ]
             }
         ],