bugfix: appointment hours now use the client timezone on UTC servers.

Logical API errors throw stable codes so users see translated messages instead of a generic bad request.

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/src/modules/prosthesis-catalog/prosthesis-catalog.service.ts

@@ -1,4 +1,5 @@
-import { Injectable, BadRequestException, OnModuleInit } from '@nestjs/common';
+import { HttpStatus, Injectable, OnModuleInit } from '@nestjs/common';
+import { AppException, ErrorCode } from '../../common/errors';
 import { CatalogEntityKind } from '@prisma/client';
 import { PrismaService } from '../../../prisma/prisma.service';
 import {
@@ -60,7 +61,7 @@ export class ProsthesisCatalogService implements OnModuleInit {
   assertKnownProsthesisType(code: string): void {
     this.ensureLoaded();
     if (!this.byCode.has(code)) {
-      throw new BadRequestException(`Unknown prosthesis type: ${code}`);
+      throw new AppException(ErrorCode.CATALOG_UNKNOWN_PROSTHESIS_TYPE, HttpStatus.BAD_REQUEST);
     }
   }