Added backups of all data, restorable on another computer (#1008)

Co-authored-by: Thorsten Sommer <SommerEngineering@users.noreply.github.com>

app/AGENTS.md

@@ -30,6 +30,8 @@ Key structure:
 - **Naming conventions** - Constants, enum members, and `static readonly` fields use `UPPER_SNAKE_CASE` such as `MY_CONSTANT`.
 - **Message Bus** - Singleton event bus for cross-component communication inside the .NET app
 - **Prompt injection reports** - The user hears once per action about what the filter removed, as soon as that action ends. Content which belongs to an action carries its scope from `PromptInjectionGuardService.BeginAction` down to where it is read or filtered; whatever is filtered without a scope is reported right away. Pass the scope as a parameter, never through a field or an `AsyncLocal`: the service serves the whole app, and the message bus delivers to other receivers in the execution context of whoever sends.
+- **Paths in stored data** - A stored path to a file which AI Studio keeps below the data directory, such as a transcript or a tokenizer copy, is relative to that directory, so that a backup or a copy of the data directory works on another computer, under another user name, or on another OS. Mark such a property with `[JsonConverter(typeof(DataDirectoryRelativePathConverter))]`, for a positional record parameter with `[property: ...]`; in memory, the path stays absolute. Better still, derive the path from IDs and store none, as `VisualBriefingStore` does. Paths to files of the user stay absolute. Chats stored before v26.10.1 are migrated by a compatibility shim, see `documentation/compatibility-shims/2026-10-relative-data-paths.md`.
+- **New files and folders in the data or configuration directory** - Whoever adds a file or folder directly to the data or configuration directory, or below `plugins/` or `databases/` one which needs a decision of its own, lists it in `DataBackupContents.ENTRIES`: as part of a backup, or with the reason a backup leaves it out. A backup takes along only what is listed as included, and a restore replaces only that. An entry included in a backup also goes into `REPLACEABLE_ELEMENTS` in `runtime/src/data_restore.rs`; otherwise the runtime refuses to restore it. The folder panel on the information page shows the list to users who back up these folders with a tool of their own.
 - **Encryption** - Initialized before Rust service is marked ready
 - **Debug environment** - Reads `startup.env` file with IPC credentials
 - **Production environment** - Runtime launches .NET sidecar with environment variables