fix: adopt sharp 0.35.2+ by centralizing the FormatEnum key type (#362)

Centralizes the sharp format key type into a single `SharpFormat` alias derived from `toFormat()`'s signature (exported from @snapotter/image-engine, imported by the API consumers), replacing the duplicated `keyof FormatEnum` definitions. Adds convert/compress format round-trip tests covering webp/avif/png/jpeg. Part of #325.

apps/api/src/lib/output-format.ts

@@ -1,6 +1,5 @@
-import sharp, { type FormatEnum } from "sharp";
-
-export type SharpFormat = Extract<keyof FormatEnum, string> | "avif";
+import type { SharpFormat } from "@snapotter/image-engine";
+import sharp from "sharp";
 
 export interface OutputFormat {
   format: SharpFormat;

apps/api/src/routes/tools/split.ts

@@ -1,8 +1,9 @@
 import { randomUUID } from "node:crypto";
 import { extname } from "node:path";
+import type { SharpFormat } from "@snapotter/image-engine";
 import archiver from "archiver";
 import type { FastifyInstance } from "fastify";
-import sharp, { type FormatEnum } from "sharp";
+import sharp from "sharp";
 import { z } from "zod";
 import { autoOrient } from "../../lib/auto-orient.js";
 import { getSecurityHeaders } from "../../lib/csp.js";
@@ -24,8 +25,6 @@ const settingsSchema = z.object({
   quality: z.number().min(1).max(100).default(90),
 });
 
-type SharpFormat = Extract<keyof FormatEnum, string> | "avif";
-
 function resolveOutputFormat(
   outputFormat: string,
   originalExt: string,