feat(ui): complete Task 4 UI redesign — all sub-tasks 1-10

- Implemented complete design system with 40+ CSS custom properties
- Created 9 UI primitives (GameCard, SectionHeader, StatRow, ManaBar, ElementBadge, ValueDisplay, ActionButton, SkillRow, TooltipInfo)
- Redesigned all tabs: Spire, Skills, Stats, Equipment, Crafting, Attunements, Golemancy, Spells, Loot, Achievements, Lab, Debug
- Added toast notification system (GameToast) with success/warning/error/info types
- Added confirmation dialogs for destructive actions
- Removed all dev artifacts and component name labels
- Added empty states to all tabs
- Replaced emoji icons with Lucide React icons
- Added enchantPower placeholder to StatsTab and EquipmentTab
- Mobile audit passed at 375px viewport
- Build passes with 0 errors, lint passes with 0 errors

Sub-tasks completed:
- ST1: Design System Implementation
- ST2: Global Layout & Header
- ST3: Left Panel (Mana Display & Action Area)
- ST4: Skills Tab
- ST5: Spire Tab & Spire Mode UI
- ST6: Stats Tab
- ST7: Equipment & Crafting Tabs
- ST8: Attunements Tab
- ST9: Remaining Tabs
- ST10: Toast System & Confirmation Dialogs

Documentation: 15+ files in docs/task4/

docs/task4/subtask_8.md

@@ -0,0 +1,38 @@
+# Sub-task 8: Enhance StatsTab & LabTab
+
+## Scope
+
+Refactor the `StatsTab` and `LabTab` components to use the new design system primitives.
+
+### Key Deliverables:
+1. Update `StatsTab` to use `GameCard`, `SectionHeader`, `StatRow`, `ValueDisplay` primitives
+2. Update `LabTab` to use `GameCard`, `SectionHeader`, `ActionButton` primitives
+3. Style stat displays with proper numeric formatting (tabular-nums)
+4. Add `ValueDisplay` for DPS, mana values
+5. Ensure all stats are clearly readable
+
+## Acceptance Criteria
+
+1. Stat rows use `StatRow` primitive with appropriate highlighting
+2. Numeric values use `ValueDisplay` with tabular-nums
+3. Section headers use `SectionHeader` primitive
+4. Stat cards use `GameCard` with appropriate variant
+5. No raw hex values - all colors use CSS variables
+6. All numbers use `--font-mono` and `tabular-nums` feature
+
+## Dependencies
+
+- **ST1 (Sub-task 1)** - Must be completed first (design system must exist)
+
+## Status
+
+🟡 **PENDING** - Waiting for ST1 completion
+
+## Notes
+
+- StatsTab location: `src/components/game/tabs/StatsTab.tsx`
+- LabTab location: `src/components/game/tabs/LabTab.tsx`
+- StatsTab shows: mana stats, combat stats, prestige stats
+- LabTab handles: research, unlocking new features
+- DPS calculation display needs proper formatting
+- Include computed stats from equipment effects