feat: +thin-client role + AZ-TC-01..03 pilot

Auf Basis des Grilling-Sessions mit 20 design decisions umgesetztes
v1-Skeleton der Thin-Client-Rolle plus 3 Pilot-Hosts.

Architektur:
- roles/thin-client/ als geschlossene Rolle (default.nix compose + 7
  Subdirectories: hardware, session, identity, network, peripherals,
  apps, monitoring, deployment)
- hosts/AZ-TC-NN/default.nix als ~20-Zeilen-Wrapper pro Fleet-Host
- flake.nix instanziiert AZ-TC-01..03 via Fleet-Helper
- secrets.nix mit per-host agenix-Secret-Stubs

Submodule:
- hardware: dell-optiplex-micro + generic-x86_64-uefi Fallback
- identity: AD (sssd/krb5/keytab via agenix), lokale Notfalluser
  (sascha.koenig + jannik.mueller ohne m3ta-home), sudo-Policy
- session: KDE Plasma 6 + Wayland + SDDM, Branding (Wallpaper + Footer),
  PipeWire Audio
- network: NetworkManager + wpa_supplicant + 802.1X EAP-TLS, NetBird
  + SSH via NetBird, systemd-resolved (Corp + NetBird DNS), hardened
  firewall, OpenSSH
- peripherals: CUPS mit Pull-Print-Queue, pam_mount für DFS-Shares
- apps: Chromium (ManagedBookmarks, Bitwarden force-install, no local
  passwords), Office-Web .desktop-Shortcuts, Remmina (mehrere TS,
  Kerberos SSO), RustDesk Client + Daemon, OBS Studio, Autostart
- monitoring: node_exporter → Pushgateway, Alloy (stub für Loki),
  Snipe-IT Asset-Checkin (stub)
- deployment: Disko BTRFS-Layout, auto-upgrade daily + reboot window,
  snapper snapshots

Build-Validierung: 'nix flake check' bestanden für AZ-TC-01/02/03.

Siehe roles/thin-client/README.md für den Provisionierungs-Workflow
und die Liste der noch auszufüllenden Platzhalter (TODO-Kommentare
in den jeweiligen Modulen).

roles/thin-client/hardware/generic-x86_64-uefi.nix

@@ -0,0 +1,26 @@
+# roles/thin-client/hardware/generic-x86_64-uefi.nix
+#
+# Fallback hardware class for any UEFI-bootable x86_64 mini-PC that isn't
+# explicitly listed. Used during pilot if a new SKU shows up, prevents
+# deploy from blocking.
+{config, lib, pkgs, ...}: {
+  config = lib.mkIf (config.az.tc.enable && config.az.tc.hardwareClass == "generic-x86_64-uefi") {
+    boot = {
+      loader.systemd-boot.enable = true;
+      loader.efi.canTouchEfiVariables = true;
+      initrd.kernelModules = ["i915" "amdgpu" "snd_hda_intel"];
+      kernelModules = ["kvm-intel" "kvm-amd" "coretemp"];
+      kernelParams = ["quiet"];
+      kernelPackages = pkgs.linuxPackages_latest;
+    };
+
+    services.xserver.videoDrivers = ["modesetting" "amdgpu"];
+
+    hardware.enableRedistributableFirmware = true;
+
+    systemd.targets.sleep.enable = false;
+    systemd.targets.suspend.enable = false;
+    systemd.targets.hibernate.enable = false;
+    systemd.targets.hybrid-sleep.enable = false;
+  };
+}