Phase 3: API Endpoint Tests - Authentication & Dictionary APIs

@babblebey is already working on this.

Since Oct 19, 2025.

**Part of:** #170
**Depends on:** #171

## 📋 Phase 3: API Endpoint Tests (High Priority)

### Scope
This phase focuses on testing all API endpoints - the external interface and user-facing functionality.

### 4. **API Routes** (`src/pages/api/`)
**Why critical**: External interface, user-facing functionality.

#### `api/dictionary.js` - Main Dictionary API
**POST endpoint (word submission)**
- [ ] Authentication validation
- [ ] Input sanitization
- [ ] Word creation flow
- [ ] Word editing flow
- [ ] Error responses

**DELETE endpoint (branch cleanup)**
- [ ] Authentication validation
- [ ] Branch deletion
- [ ] Error handling

#### `api/github/oauth/` - Authentication
- [ ] OAuth authorization flow
- [ ] Callback handling
- [ ] Token validation
- [ ] Error scenarios

#### `api/v1/browse/` - Browse Functionality
- [ ] Dictionary browsing endpoints
- [ ] Pagination logic
- [ ] Search functionality
- [ ] Error handling

## 🎯 Success Criteria
- 70%+ coverage for API endpoints
- All authentication flows tested
- Input validation thoroughly tested
- Error scenarios properly handled
- Security validation for auth flows

## 📅 Timeline
**Week 3** of testing implementation

## 🛠️ Setup Required
- Set up API testing framework
- Mock external GitHub API calls
- Create test database/fixtures
- Set up authentication mocking