Fix Blackwell GPU driver: open kernel modules, bump pin to 595

The gpu role pinned nvidia-driver-580-server (proprietary kernel
modules). Those install and load cleanly on the RTX PRO 6000, but the
GPU never initialises: NVRM fails at RmInitAdapter (0x22:0x56:897) and
nvidia-smi reports "No devices were found". Blackwell (10de:2bb5)
requires the open kernel modules.

- defaults/main.yml: nvidia-driver-580-server -> 595-server-open.
  The "-open" part is the actual fix and is version independent. 595 is
  the newest -server branch in the 24.04 archive (610 is desktop only);
  projektplan §5.3 asked for the branch to be re-checked and pinned at
  install time, which had not happened yet. Caveat noted in the file:
  595 ships from multiverse, 580/590 from restricted.
- tasks/main.yml: install_recommends: false, keeps nvidia-settings and
  its GTK chain off a headless server (~65 packages).
- manuals/20260714-nvidia-driver-install.md: same command, documents
  the open-module requirement and the failure signature.
- SETUP.md: tick off the completed OS install steps.

Verified on phy-z-srv-gpu01: driver 595.71.05, CUDA 13.2, RTX PRO 6000
Blackwell at 00000001:5C:00.0 with 97887MiB visible, no NVRM errors in
dmesg, single DKMS version registered.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

ansible/roles/nvidia_gpu/tasks/main.yml

@@ -17,6 +17,7 @@
   apt:
     name: "{{ nvidia_driver_package }}"
     state: present
+    install_recommends: false
   register: nvidia_driver_install
 
 - name: Reboot after fresh driver install