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/todo.md

@@ -0,0 +1,61 @@
+# Task 4 - Overall TODO Tracker
+
+## All Sub-tasks: ✅ COMPLETED
+
+- [x] **Sub-task 1:** Design System Implementation ✅ COMPLETED
+- [x] **Sub-task 2:** Global Layout & Header ✅ COMPLETED
+- [x] **Sub-task 3:** Left Panel (Mana Display & Action Area) ✅ COMPLETED
+- [x] **Sub-task 4:** Skills Tab ✅ COMPLETED
+- [x] **Sub-task 5:** Spire Tab & Spire Mode UI ✅ COMPLETED
+- [x] **Sub-task 6:** Stats Tab ✅ COMPLETED
+- [x] **Sub-task 7:** Equipment & Crafting Tabs ✅ COMPLETED
+- [x] **Sub-task 8:** Attunements Tab ✅ COMPLETED
+- [x] **Sub-task 9:** Remaining Tabs ✅ COMPLETED
+- [x] **Sub-task 10:** Toast System & Confirmation Dialogs ✅ COMPLETED
+
+## Step 5: Mobile Layout Audit ✅ COMPLETED
+- [x] Audit all tabs at 375px viewport
+- [x] Verify touch targets (44×44px)
+- [x] Check no horizontal scroll
+- [x] Document findings in `mobile_audit.md`
+
+## Step 6: Performance Check ✅ COMPLETED
+- [x] Run `npm run build` - 0 TypeScript errors ✅
+- [x] Run `npm run lint` - 0 ESLint errors ✅
+- [x] Verify CSS transitions used (not JS animations)
+- [x] Document in `performance_check.md`
+
+## Step 7: Final Audit ✅ COMPLETED
+- [x] Create `ui_audit_report.md`
+- [x] Document visual inconsistencies resolved
+- [x] Document UX friction points addressed
+- [x] Flag remaining issues with priority
+
+## Deliverables Checklist ✅ ALL COMPLETE
+
+- [x] `docs/task4/orient.md` — initial codebase survey
+- [x] `docs/task4/design_system.md` — all design decisions documented
+- [x] `src/app/globals.css` — all CSS custom properties defined
+- [x] `src/components/ui/` — all 9 primitives implemented
+- [x] All dev labels removed from rendered output
+- [x] Sub-task docs (1–10) with progress files
+- [x] `docs/task4/todo.md` updated throughout
+- [x] `docs/task4/mobile_audit.md` — mobile pass findings
+- [x] `docs/task4/ui_audit_report.md` — final audit
+- [x] Toast system wired to all destructive and error actions
+- [x] Confirm dialogs on item deletion, study cancel, prepare on enchanted item
+- [x] `enchantPower` placeholder StatRow present in StatsTab/EquipmentTab
+- [x] Consistent Lucide icons throughout (no emoji icons)
+- [x] `npm run build` passes with 0 new errors
+- [x] `npm run lint` passes with 0 new errors
+
+## Progress Summary
+
+- **Completed:** 10/10 sub-tasks (100%)
+- **Build Status:** ✅ Passing (0 errors)
+- **Lint Status:** ✅ Passing (0 errors)
+- **Documentation:** ✅ All files complete
+
+## Final Status: ✅ TASK 4 COMPLETE
+
+All sub-tasks completed. All documentation in place. Ready for production deployment.