feat(viewer): keep the user's viewer settings

apps/viewer/appinfo/info.xml

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+<?xml version="1.0"?>
+<!--
+  - SPDX-FileCopyrightText: 2026 Nextcloud GmbH and Nextcloud contributors
+  - SPDX-License-Identifier: AGPL-3.0-or-later
+-->
+<info xmlns:xsi= "http://www.w3.org/2001/XMLSchema-instance"
+	  xsi:noNamespaceSchemaLocation="https://apps.nextcloud.com/schema/apps/info.xsd">
+	<id>viewer</id>
+	<name>Viewer</name>
+	<summary>Simple file viewer with slideshow for media</summary>
+	<description><![CDATA[Show your latest holiday photos and videos like in the movies, show a glimpse of your latest novel directly from your Nextcloud, choose the best GIF of your collection thanks to the direct preview of your favorites files and many more!]]></description>
+	<version>9.0.0-dev.0</version>
+	<licence>agpl</licence>
+	<author>John Molakvoæ</author>
+	<namespace>Viewer</namespace>
+	<category>tools</category>
+	<bugs>https://github.com/nextcloud/server/issues</bugs>
+	<dependencies>
+		<nextcloud min-version="36" max-version="36"/>
+	</dependencies>
+</info>

apps/viewer/composer/autoload.php

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+<?php
+
+// autoload.php @generated by Composer
+
+if (PHP_VERSION_ID < 50600) {
+    if (!headers_sent()) {
+        header('HTTP/1.1 500 Internal Server Error');
+    }
+    $err = 'Composer 2.3.0 dropped support for autoloading on PHP <5.6 and you are running '.PHP_VERSION.', please upgrade PHP or use Composer 2.2 LTS via "composer self-update --2.2". Aborting.'.PHP_EOL;
+    if (!ini_get('display_errors')) {
+        if (PHP_SAPI === 'cli' || PHP_SAPI === 'phpdbg') {
+            fwrite(STDERR, $err);
+        } elseif (!headers_sent()) {
+            echo $err;
+        }
+    }
+    throw new RuntimeException($err);
+}
+
+require_once __DIR__ . '/composer/autoload_real.php';
+
+return ComposerAutoloaderInitViewer::getLoader();

apps/viewer/composer/composer.json

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+{
+    "config" : {
+        "vendor-dir": ".",
+        "optimize-autoloader": true,
+        "classmap-authoritative": true,
+        "autoloader-suffix": "Viewer"
+    },
+    "autoload" : {
+        "psr-4": {
+            "OCA\\Viewer\\": "../lib/"
+        }
+    }
+}