refactor(api): alle handler auf api-helpers umstellen

13 +server.ts handler nutzen jetzt parsePositiveIntParam und
validateBody statt jeweils lokaler parseId/safeParse-Bloecke.

Konsequenzen:
- 9 lokale parseId/parsePositiveInt Definitionen geloescht
- 11 safeParse + manueller error()-Throws ersetzt
- domains/[id], domains, profiles: catch-Block reicht jetzt HttpError
  durch (isHttpError) — vorher wurde ein 404 vom updateDomain als 409
  re-emittiert
- recipes/[id]/image: kein function-clutter mehr neben den FormData-Pfaden
- Konsistente Error-Bodies: validateBody schickt {message, issues},
  parsePositiveIntParam {message: 'Missing X' / 'Invalid X'}

Findings aus REVIEW-2026-04-18.md (Refactor A) und redundancy.md

src/routes/api/recipes/[id]/image/+server.ts

@@ -5,6 +5,7 @@ import { existsSync } from 'node:fs';
 import { mkdir, writeFile } from 'node:fs/promises';
 import { join } from 'node:path';
 import { getDb } from '$lib/server/db';
+import { parsePositiveIntParam } from '$lib/server/api-helpers';
 import { getRecipeById, updateImagePath } from '$lib/server/recipes/repository';
 
 const IMAGE_DIR = process.env.IMAGE_DIR ?? './data/images';
@@ -19,14 +20,8 @@ const EXT_BY_MIME: Record<string, string> = {
   'image/avif': '.avif'
 };
 
-function parseId(raw: string): number {
-  const id = Number(raw);
-  if (!Number.isInteger(id) || id <= 0) error(400, { message: 'Invalid id' });
-  return id;
-}
-
 export const POST: RequestHandler = async ({ params, request }) => {
-  const id = parseId(params.id!);
+  const id = parsePositiveIntParam(params.id, 'id');
   const db = getDb();
   if (!getRecipeById(db, id)) error(404, { message: 'Recipe not found' });
 
@@ -53,7 +48,7 @@ export const POST: RequestHandler = async ({ params, request }) => {
 };
 
 export const DELETE: RequestHandler = ({ params }) => {
-  const id = parseId(params.id!);
+  const id = parsePositiveIntParam(params.id, 'id');
   const db = getDb();
   if (!getRecipeById(db, id)) error(404, { message: 'Recipe not found' });
   updateImagePath(db, id, null);