docs(portable-mode): add documentation for portable mode

- describe portable mode features and benefits
- explain how to enable portable mode via ENV.ini
- include notes about first launch and platform support
- provide details on disabling portable mode

1 files changed, 65 insertions, 0 deletions

diff --git a/src/content/docs/advanced/portable-mode.md b/src/content/docs/advanced/portable-mode.md
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+---
+title: "Portable Mode"
+sidebar:
+  label: Portable Mode
+  order: 1
+---
+
+GpgFrontend offers a Portable Mode to provide users with maximum flexibility and
+convenience, particularly for running the application from removable storage
+devices (such as USB drives) or non-standard locations, without leaving traces
+on the host system.
+
+When Portable Mode is enabled, GpgFrontend stores all user data, configuration
+files, secure keys, logs, and other runtime files directly within the
+application’s directory structure, rather than using the system’s default user
+data folders. This design allows users to move or back up the entire application
+and its environment easily.
+
+> Note: Starting from version 2.1.9, Portable Mode is enabled by adding
+> PortableMode=true to the ENV.ini file in the working directory. In earlier
+> versions (prior to v2.1.9), Portable Mode was activated by creating an empty
+> file named PORTABLE.txt in the working directory.
+
+## Key Features
+
+- **Self-Contained Environment:** All configuration, logs, application data
+  (data_objs/), secure keys, and modules are stored within the portable
+  directory. Nothing is written to system user directories.
+
+- **No System Traces:** Running in Portable Mode avoids leaving personal or
+  sensitive data on the host system, making it ideal for shared or temporary
+  environments.
+
+- **Cross-Platform Consistency:** Portable Mode works consistently across
+  supported operating systems, including Windows, Linux, and macOS (AppImage,
+  Flatpak, etc.).
+
+## **How to Enable Portable Mode**
+
+Portable Mode can be enabled via the application’s configuration:
+
+1. In the application’s working directory, create or edit the file ENV.ini.
+2. Add the following line to the file:
+
+   ```ini
+   PortableMode=true
+   ```
+
+3. Save the file and restart GpgFrontend.
+
+Once enabled, the application will operate entirely in Portable Mode, with all
+files stored relative to the application’s own directory.
+
+## Notes
+
+- **First Launch:** You can enable Portable Mode at any time, but it is
+  recommended to do so before initial setup to ensure all data is stored
+  portably from the beginning.
+- **AppImage/Flatpak Support:** On Linux, GpgFrontend can detect and adapt to
+  being run as an AppImage or within a Flatpak container, and will place user
+  data within the application directory accordingly.
+- **Disabling Portable Mode:** To revert to standard mode, simply set
+  PortableMode=false in the ENV.ini file or remove the line, then restart the
+  application. Data previously stored in portable locations will remain, but new
+  data will be saved to the default system directories.