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/local_watchdog.py

@@ -2,7 +2,7 @@
 
 VM idle-killer remains the default safety net. This module is opt-in via
 `gpu-rent watchdog install`: while a tunnel is armed, a scheduled tick stops
-compute if the laptop/process died without Ctrl+C detach or `gpu-rent stop`.
+compute if the laptop/process died without Ctrl+C/Ctrl+D ``stop`` or `gpu-rent stop`.
 """
 
 from __future__ import annotations
@@ -189,7 +189,7 @@ def touch_heartbeat() -> None:
 
 
 def detach_lease_keep_gpu() -> None:
-    """Ctrl+C on tunnel: leave GPU running; local tick must not stop."""
+    """Mark the lease detached so the local tick will not stop compute."""
     lease = load_lease()
     if lease is None:
         lease = LocalLease()
@@ -271,7 +271,7 @@ def install_watchdog(
     log(
         f"local-watchdog установлен ({platform}): тик каждые {interval} мин. "
         f"Grace {grace_seconds() // 60} мин после смерти процесса туннеля → stop. "
-        f"Ctrl+C на туннеле GPU не гасит; Ctrl+D — stop. "
+        f"Ctrl+C / Ctrl+D на туннеле — stop. "
         "При SELECTEL_API_TOKEN — toast каждые BALANCE_NOTIFY_STEP_RUB ₽ (дефолт 200)."
     )
     return marker