Update documentation to clarify GPU control commands

- Revised README, architecture, CLI, and other documentation to specify that both `Ctrl+C` and `Ctrl+D` now stop the GPU while preserving disk data, correcting previous inaccuracies.
- Enhanced access card and setup instructions to reflect the updated command behavior for better user understanding.
- Updated tests to ensure the new command behaviors are validated and documented correctly, improving overall clarity in GPU management.

src/gpu_rent/access_card.py

@@ -125,8 +125,7 @@ def render_access_panel(
     cmds.add_row("hold killer", "gpu-rent hold")
     cmds.add_row("стоп GPU", "gpu-rent stop")
     if tunneled:
-        cmds.add_row("Ctrl+C", "туннель off, GPU жив")
-        cmds.add_row("Ctrl+D", "stop GPU, диски остаются")
+        cmds.add_row("Ctrl+C / Ctrl+D", "stop GPU, диски остаются")
     if not tunneled:
         cmds.add_row("туннель", "gpu-rent tunnel --open")
 
@@ -220,7 +219,7 @@ def print_access_card(
         for line in mcp_snippet_lines(cfg):
             log(line)
         log("hold: gpu-rent hold   |  stop: gpu-rent stop")
-        log("Ctrl+C — туннель off, GPU жив  |  Ctrl+D — stop GPU")
+        log("Ctrl+C / Ctrl+D — stop GPU (диски остаются)")
         log("")
         return
     from gpu_rent.term import console as default_console