Answer an oversized photo with the reason, not a 500

A file past the size limit makes the multipart stream itself throw, which
escaped the per-file catch and reached the error handler: the phone that just
sent a 35 MB photo got 'Something went wrong'. Catch the limit errors around the
part loop, say which limit was hit, and report it once rather than twice. Also
asserts that derivatives carry no EXIF while the Original keeps the uploaded
bytes.

src/server.ts

@@ -98,6 +98,7 @@ export async function buildApp(options: AppOptions): Promise<FastifyInstance> {
     sessionSecret: options.sessionSecret,
     adminPasswordHash: options.adminPasswordHash,
     secureCookies: options.secureCookies,
+    maxUploadBytes: options.config.limits.maxUploadBytes,
     throttle: options.throttle,
   });