docs(faq): update FTP/SFTP section for async upload queue

- Remove obsolete 'folder' and 'urlTemplate' config fields
- Document SFTP support and type selector
- Explain async upload queue (SQLite-backed, background worker)
- Add systemd service setup and manual worker commands
- Describe random remote filenames, directory listing protection
- Document automatic QR URL building (no template needed)
- Describe online gallery features: spinner, share button, lightbox nav
- Add 'Delete on local delete' subsection

Author: flacoonb

docs/faq/index.md

@@ -356,38 +356,71 @@ and enter/adjust the @chromium-browser entries as followed (adjust the value _19
 
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-## How does the connection to the FTP server work?
+## How does the connection to the FTP/SFTP server work?
 
-The connection to the FTP server needs 4 distinct properties.
+### Connection settings
 
--   `baseURL` which is the url where all requests will be made
--   `port` for ssl connection (the default value is 21)
--   `username` the username of the user authorized to interact to the FTP server
--   `password` the password of the user
+The following properties are required to connect to the remote server:
 
-With these four variables you can test the connection to the FTP server to check if everything is alright.
+-   `type` — protocol: `ftp` (default) or `sftp`
+-   `baseURL` — hostname or IP address of the server
+-   `port` — port number (default: `21` for FTP, `22` for SFTP)
+-   `username` — username authorized to access the server
+-   `password` — password for that user (stored encrypted on disk)
 
-The next variables are for the place where you want the pictures to be stored:
+Use **Test Connection** in the admin panel to verify the credentials before saving.
 
--   `baseFolder` is the folder of your website (if you have multiple websites living on the server with this property you can choose on which of these the file should be stored)
--   `folder` the folder dedicated to the upload of the files
--   `title` if you are doing an event you can set the title of the event to create another folder (the system will slugify the string)
+### Storage location
 
-In the end the processed picture, and the thumbnails, will be uploaded in the folder according to these variables.
+-   `baseFolder` — root folder on the server where all files are stored (e.g. `photobooth` or `www/gallery`). You can browse available folders using the folder picker in the admin panel.
+-   `title` — optional event title; used as the page title of the online gallery
 
-If you have a website, you can use the following variables to generate the qr codes that will point to the photos uploaded to the ftp server
+Photos are stored inside `<baseFolder>/images/` and thumbnails inside `<baseFolder>/thumbs/` using privacy-preserving random filenames so the original file names are never exposed on the server.
 
--   `useForQr` to enable this functionality
--   `website` accessible from the internet, it will be the base of the qr code link
--   `urlTemplate` starting from the previous set of variables, you have to define the template which will be used to generate the qrcode link (each variable should be written whit '%' before e.g. %website/%folder/%date)
+### QR code integration
 
-Last but not least you can upload a php file on the `title` folder on the FTP server to create an online gallery which is updated with every new picture (and collage) taken.
-The variable to manage this feature are the following:
+-   `useForQr` — when enabled, QR codes point to the remote gallery instead of the local Photobooth
+-   `website` — publicly accessible base URL of the remote server (e.g. `https://example.com`)
 
--   `create_webpage` to enable this functionality
--   `template_location` which is the location of the index.php file, which is formatted with the title of the current event and uploaded to the FTP server
+The QR code URL is built automatically as `<website>/<baseFolder>/?img=<remote-filename>`. No manual URL template is required.
 
-In the end you can enable the `delete` functionality that will delete photos (and collages) from the ftp server when they are deleted from the photobooth gallery (no admin reset)
+### Online gallery
+
+-   `create_webpage` — when enabled, Photobooth uploads a ready-to-use PHP gallery (`index.php` and `config.inc.php`) to the `baseFolder` on the server. The gallery is updated with every new photo.
+-   `template_location` — path to the local `index.php` template that is uploaded (default: `resources/template/index.php`)
+
+The gallery shows photos sorted newest-first and supports single-image deep links via `?img=<filename>`. While a photo is still being uploaded the visitor sees a spinner; the page reloads automatically once the image is available. A native share button (Web Share API) and a lightbox with keyboard navigation are included.
+
+Directory listing for `images/` and `thumbs/` is blocked by `index.php` redirect guards that are uploaded automatically.
+
+### Async upload queue
+
+Uploads run **asynchronously** in a background worker so the Photobooth UI is never blocked while files are transferred. After a photo is taken, a job is added to a local SQLite queue. The worker processes jobs one by one and retries up to 5 times on failure.
+
+To run the worker as a persistent background service, copy the provided systemd unit and enable it:
+
+```bash
+sudo cp resources/config/photobooth-upload-worker.service /etc/systemd/system/
+sudo systemctl daemon-reload
+sudo systemctl enable --now photobooth-upload-worker
+sudo systemctl status photobooth-upload-worker
+```
+
+The worker can also be run manually for testing:
+
+```bash
+# Process all pending jobs once and exit
+sudo -u www-data php bin/photobooth photobooth:upload:worker --once
+
+# Run continuously (polls every 5 seconds)
+sudo -u www-data php bin/photobooth photobooth:upload:worker
+```
+
+Upload queue status (pending jobs, failed jobs) is visible in the Photobooth debug panel.
+
+### Delete on local delete
+
+Enable `delete` to automatically remove the photo and thumbnail from the FTP/SFTP server whenever a photo is deleted from the local Photobooth gallery (does not apply to admin reset).
 
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