App store listing: screenshots, links and UI fixes

Add three screenshots (backups, restore, settings) taken on a demo
instance, plus website, repository and the HOWTO as admin documentation
in info.xml.

Fixes found while taking them:
- the "new folder" restore option lost "<date>" (l10n sanitizes it as
  a tag); show the folder name pattern via a placeholder instead
- the restore-point dropdown cut off the time
- passphrase actions stacked vertically in the slot table
- HOWTO: SFTP example used "sftp::password", the auth mechanism is
  "password::password"

appinfo/info.xml

@@ -13,8 +13,16 @@ See the README for known limitations and the recovery kit before relying on it.]
     <licence>agpl</licence>
     <author>Dillard Blom</author>
     <namespace>NgBackup</namespace>
+    <documentation>
+        <admin>https://github.com/dillardblom/ng_backup/blob/main/docs/HOWTO.md</admin>
+    </documentation>
     <category>tools</category>
+    <website>https://apps.nextcloud.com/apps/ng_backup</website>
     <bugs>https://github.com/dillardblom/ng_backup/issues</bugs>
+    <repository type="git">https://github.com/dillardblom/ng_backup</repository>
+    <screenshot>https://raw.githubusercontent.com/dillardblom/ng_backup/main/screenshots/1-backups.png</screenshot>
+    <screenshot>https://raw.githubusercontent.com/dillardblom/ng_backup/main/screenshots/2-restore.png</screenshot>
+    <screenshot>https://raw.githubusercontent.com/dillardblom/ng_backup/main/screenshots/3-settings.png</screenshot>
     <dependencies>
         <php min-version="8.1"/>
         <lib>sodium</lib>