Update documentation and CLI behavior for GPU management

- Clarified the behavior of `Ctrl+C` and `Ctrl+D` in the README and other documentation, specifying that `Ctrl+C` only stops the tunnel while keeping the GPU active, and `Ctrl+D` stops the GPU while preserving disk data.
- Enhanced the CLI documentation to reflect these changes, ensuring users understand the implications of these commands during GPU operations.
- Improved the handling of data bindings and remounting logic in the codebase to prevent issues with empty model tabs in the UI.
- Added tests to validate the new command behaviors and ensure proper documentation alignment.

docs/spike-notes.md

@@ -63,12 +63,14 @@
 
 ## 3. Туннель и API
 
-Если закрыл туннель (Ctrl+C):
+Если закрыл туннель (**Ctrl+C**, GPU жив):
 
 ```powershell
 .\gpu-rent.ps1 tunnel --open
 ```
 
+**Ctrl+D** на живом туннеле = `stop` GPU.
+
 | Шаг | OK? |
 | --- | --- |
 | UI http://127.0.0.1:17801 | |