Refactor .NET installation logic in bootstrap script

- Changed the check for the existence of the .NET installation script to verify if the file exists instead of checking for execution permissions.
- Updated the command to run the .NET installation script from the repository root to ensure proper execution context.
- Added error handling to log a warning if the installation script fails and an error message if .NET is still not installed after the attempt, preventing SwarmUI from starting.
- Enhanced logging to confirm successful .NET installation, improving user feedback during the bootstrap process.

src/gpu_rent/remote/bootstrap.sh

@@ -150,11 +150,20 @@ else
 fi
 
 if [[ ! -x /usr/share/dotnet/dotnet && ! -x "/home/${SWARM_USER}/.dotnet/dotnet" ]]; then
-  if [[ -x "${SWARM_ROOT}/launchtools/linux-dotnet-install.sh" ]]; then
+  if [[ -f "${SWARM_ROOT}/launchtools/linux-dotnet-install.sh" ]]; then
     log "ставим .NET SDK (скрипт SwarmUI)"
-    sudo -u "$SWARM_USER" bash "${SWARM_ROOT}/launchtools/linux-dotnet-install.sh" || true
+    # SwarmUI's linux-dotnet-install.sh does `cd launchtools` and
+    # `./launchtools/dotnet-install.sh` — must run from repo root.
+    if ! sudo -u "$SWARM_USER" bash -c "cd \"$SWARM_ROOT\" && bash launchtools/linux-dotnet-install.sh"; then
+      log "WARN: linux-dotnet-install.sh завершился с ошибкой"
     fi
   fi
+  if [[ ! -x /usr/share/dotnet/dotnet && ! -x "/home/${SWARM_USER}/.dotnet/dotnet" ]]; then
+    log "ERROR: .NET не установлен ($HOME/.dotnet или /usr/share/dotnet) — SwarmUI не стартует"
+    exit 1
+  fi
+  log ".NET ok: $(sudo -u "$SWARM_USER" bash -lc 'command -v dotnet || echo /home/'"$SWARM_USER"'/.dotnet/dotnet')"
+fi
 
 mkdir -p \
   "${SWARM_ROOT}/Models" \