feat: Add backend support for measurement unit preferences

Updated backend to support measurement unit preferences (Metric/Imperial)
in user profiles. The preferences are stored in the existing JSONB
preferences column, which already exists in the database.

**Backend Changes:**
- Updated User entity to include measurementUnit in preferences type
- Created UpdateProfileDto with proper validation for preferences
- Updated auth controller to use UpdateProfileDto for PATCH /api/v1/auth/profile
- Added IsIn validator for measurementUnit ('metric' | 'imperial')

**Documentation:**
- Updated LOCALIZATION_IMPLEMENTATION_PLAN.md with completion status
- Marked Phases 1, 2, 3, 7, 8 as completed
- Marked Phase 4 (backend preferences) as in progress
- Added detailed completion markers for each subsection

**Technical Details:**
- No migration needed - using existing preferences JSONB column
- Preferences object now includes: notifications, emailUpdates, darkMode, measurementUnit
- Endpoint: PATCH /api/v1/auth/profile accepts optional preferences object
- Validation ensures measurementUnit is either 'metric' or 'imperial'

**Next Steps:**
- Frontend integration to persist language/measurement preferences to backend
- Apply localization throughout remaining pages and components
- Create onboarding flow with language/measurement selection

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

maternal-app/maternal-app-backend/src/database/entities/user.entity.ts

@@ -91,6 +91,7 @@ export class User {
     notifications?: boolean;
     emailUpdates?: boolean;
     darkMode?: boolean;
+    measurementUnit?: 'metric' | 'imperial';
   };
 
   @CreateDateColumn({ name: 'created_at' })

maternal-app/maternal-app-backend/src/modules/auth/auth.controller.ts

@@ -24,6 +24,7 @@ import { RegisterDto } from './dto/register.dto';
 import { LoginDto } from './dto/login.dto';
 import { RefreshTokenDto } from './dto/refresh-token.dto';
 import { LogoutDto } from './dto/logout.dto';
+import { UpdateProfileDto } from './dto/update-profile.dto';
 import {
   RequestPasswordResetDto,
   ResetPasswordDto,
@@ -88,7 +89,7 @@ export class AuthController {
   @HttpCode(HttpStatus.OK)
   async updateProfile(
     @CurrentUser() user: any,
-    @Body() updateData: { name?: string },
+    @Body() updateData: UpdateProfileDto,
   ) {
     return await this.authService.updateProfile(user.userId, updateData);
   }

maternal-app/maternal-app-backend/src/modules/auth/dto/update-profile.dto.ts

@@ -0,0 +1,33 @@
+import { IsString, IsOptional, IsObject, ValidateNested, IsIn } from 'class-validator';
+import { Type } from 'class-transformer';
+
+export class UserPreferencesDto {
+  @IsOptional()
+  notifications?: boolean;
+
+  @IsOptional()
+  emailUpdates?: boolean;
+
+  @IsOptional()
+  darkMode?: boolean;
+
+  @IsOptional()
+  @IsIn(['metric', 'imperial'])
+  measurementUnit?: 'metric' | 'imperial';
+}
+
+export class UpdateProfileDto {
+  @IsOptional()
+  @IsString()
+  name?: string;
+
+  @IsOptional()
+  @IsString()
+  locale?: string;
+
+  @IsOptional()
+  @IsObject()
+  @ValidateNested()
+  @Type(() => UserPreferencesDto)
+  preferences?: UserPreferencesDto;
+}