docs: move completed frontend refactoring to COMPLETED.md

Moved the entire frontend refactoring section (3 phases + bug fixes)
from TODO.md to docs/archive/COMPLETED.md for better organization.

Changes:
- TODO.md: Removed completed refactoring tasks (lines 363-728)
- COMPLETED.md: Added comprehensive refactoring summary with:
  - All 3 phases (Components, Hooks, Advanced Components)
  - Bug fixes (formatHeat, ChatRoom missing)
  - Final metrics (-559 lines, 16 new components, 3 new hooks)
  - Component structure diagram

docs/archive/COMPLETED.md

@@ -548,6 +548,150 @@ docs: update TODO.md with completed tasks and next steps
 
 ---
 
+## ⚛️ FRONTEND REFACTORING (COMPLETED 2025-11-21)
+
+**Status:** All 3 phases completed
+**Time Spent:** ~8 hours total
+**Impact:** -559 lines of code (-17% reduction)
+**Result:** Cleaner, more maintainable codebase with reusable components
+
+### 📊 Refactoring Results
+
+**Before:**
+- Total LOC: ~4000
+- Duplicated code: ~40%
+- Largest component: 761 lines (EventChatPage)
+- Reusable components: 8
+- Custom hooks: 1
+
+**After:**
+- Total LOC: ~3441 (-559 lines, -17%)
+- Duplicated code: ~10%
+- Largest component: 471 lines (EventChatPage, -38%)
+- Reusable components: 24 (+16)
+- Custom hooks: 4 (+3)
+
+### ✅ Phase 1: Reusable Components
+**Impact:** -221 lines
+**Date:** 2025-11-21
+
+**Components Created:**
+- ✅ `components/common/Alert.jsx` - Unified alerts
+- ✅ `components/common/FormInput.jsx` - Text/email/password inputs
+- ✅ `components/common/LoadingButton.jsx` - Button with loading state
+- ✅ `components/events/EventCard.jsx` - Event list card
+- ✅ `components/modals/Modal.jsx` - Generic modal wrapper
+- ✅ `components/modals/ConfirmationModal.jsx` - Confirmation dialog
+- ✅ `components/chat/ChatMessageList.jsx` - Message list container
+- ✅ `components/chat/ChatInput.jsx` - Message input field
+
+**Pages Refactored:**
+- LoginPage: 105 → 96 lines (-9, -8.6%)
+- RegisterPage: 476 → 414 lines (-62, -13%)
+- EventChatPage: 761 → 661 lines (-100, -13%)
+- MatchChatPage: 567 → 517 lines (-50, -8.8%)
+
+**Commit:** `dea9d70` - "refactor(frontend): integrate reusable components across all pages"
+
+### ✅ Phase 2: Custom Hooks
+**Impact:** -168 lines
+**Date:** 2025-11-21
+
+**Hooks Created:**
+- ✅ `hooks/useForm.js` (82 lines) - Generic form state management
+- ✅ `hooks/useEventChat.js` (156 lines) - Event chat Socket.IO logic
+- ✅ `hooks/useMatchChat.js` (115 lines) - Match chat Socket.IO logic
+
+**Pages Refactored:**
+- EventChatPage: 661 → 564 lines (-97, -14.7%)
+- MatchChatPage: 517 → 446 lines (-71, -13.7%)
+
+**Commit:** `9e74343` - "refactor(frontend): Phase 2 - extract business logic into custom hooks"
+
+### ✅ Phase 3: Advanced Components
+**Impact:** -170 lines
+**Date:** 2025-11-21
+
+**Components Created:**
+- ✅ `components/heats/HeatBadges.jsx` (67 lines) - Heat display badges
+- ✅ `components/users/UserListItem.jsx` (93 lines) - User list entry
+- ✅ `components/events/ParticipantsSidebar.jsx` (103 lines) - Event participants sidebar
+- ✅ `components/webrtc/FileTransferProgress.jsx` (95 lines) - WebRTC file transfer UI
+- ✅ `components/webrtc/LinkShareInput.jsx` (70 lines) - Link sharing fallback
+
+**Pages Refactored:**
+- EventChatPage: 564 → 471 lines (-93, -16.5%)
+- MatchChatPage: 446 → 369 lines (-77, -17.3%)
+
+**Commit:** `082105c` - "refactor(frontend): Phase 3 - create advanced composite components"
+
+### 🐛 Bug Fixes (2025-11-21)
+
+**Frontend Bug:**
+- ✅ Fixed `formatHeat is not defined` error in EventChatPage header
+  - Enhanced HeatBadges with `badgeClassName` prop for custom styling
+  - Replaced manual heat rendering with HeatBadges component
+  - Commit: `ade5190`
+
+**Backend Bug:**
+- ✅ Fixed "Chat room not found" error when sending messages
+  - Event "Another Dance Event" was missing ChatRoom (created manually: ID 222)
+  - Added auto-creation of ChatRoom on first check-in (defensive fix)
+  - Future events will automatically have ChatRooms created
+  - All 223 backend tests still passing
+  - Commit: `198c216`
+
+### 📦 Final Component Structure
+
+```
+frontend/src/
+├── components/
+│   ├── common/
+│   │   ├── Alert.jsx ✅
+│   │   ├── Avatar.jsx
+│   │   ├── FormInput.jsx ✅
+│   │   ├── LoadingButton.jsx ✅
+│   │   ├── PasswordStrengthIndicator.jsx
+│   │   └── VerificationBanner.jsx
+│   ├── chat/
+│   │   ├── ChatMessageList.jsx ✅
+│   │   └── ChatInput.jsx ✅
+│   ├── events/
+│   │   ├── EventCard.jsx ✅
+│   │   └── ParticipantsSidebar.jsx ✅
+│   ├── heats/
+│   │   ├── HeatsBanner.jsx
+│   │   └── HeatBadges.jsx ✅
+│   ├── users/
+│   │   └── UserListItem.jsx ✅
+│   ├── webrtc/
+│   │   ├── FileTransferProgress.jsx ✅
+│   │   └── LinkShareInput.jsx ✅
+│   ├── modals/
+│   │   ├── Modal.jsx ✅
+│   │   └── ConfirmationModal.jsx ✅
+│   ├── layout/
+│   ├── pwa/
+│   └── WebRTCWarning.jsx
+├── hooks/
+│   ├── useForm.js ✅
+│   ├── useEventChat.js ✅
+│   ├── useMatchChat.js ✅
+│   └── useWebRTC.js
+```
+
+### 📊 Benefits Achieved
+
+1. ✅ **Code Reduction:** 559 lines removed (-17%)
+2. ✅ **Eliminated Duplication:** From ~40% to ~10%
+3. ✅ **Component Modularity:** 16 new reusable components
+4. ✅ **Separation of Concerns:** Business logic extracted to hooks
+5. ✅ **Maintainability:** Changes in one place affect all uses
+6. ✅ **Testability:** Smaller, focused components easier to test
+7. ✅ **Development Speed:** Future features 30-50% faster to implement
+
+---
+
 ## 📊 Statistics
 
 **Frontend:**