Add NixOS configuration for ringtail workstation (#207)

## Summary
- NixOS flake for ringtail (gaming/compute workstation, RTX 4080) in `nixos/ringtail/`
- Declarative disk partitioning via disko (GPT, 512M EFI + ext4 root on NVMe)
- NVIDIA proprietary drivers, sway/Wayland desktop, greetd, PipeWire, Steam
- Tailscale integration for tailnet connectivity
- Ansible playbook + `mise run provision-ringtail` for ongoing management
- Pulumi auth key (`tag:homelab`, `tag:blumeops`) for tailnet bootstrap

## Deployment Order
1. **Merge PR**
2. `pulumi up` in tailscale stack → creates auth key
3. Retrieve auth key: `pulumi stack output ringtail_authkey --show-secrets`
4. On ringtail NixOS installer:
   - `nix run github:nix-community/disko -- --mode disko /tmp/disk-config.nix` (or from cloned repo)
   - `nixos-install --flake github:eblume/blumeops?dir=nixos/ringtail#ringtail`
5. Reboot, `tailscale up --auth-key=<key>`
6. Verify: `tailscale status`, SSH from gilbert

## Test plan
- [ ] Review NixOS configuration for completeness
- [ ] Verify disko partition layout matches ringtail hardware
- [ ] Run `pulumi preview` for tailscale stack
- [ ] Install NixOS on ringtail
- [ ] Confirm tailscale connectivity
- [ ] Confirm sway desktop works
- [ ] Test `mise run provision-ringtail` for ongoing management

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Reviewed-on: https://forge.ops.eblu.me/eblume/blumeops/pulls/207

nixos/ringtail/disk-config.nix

@@ -0,0 +1,84 @@
+{
+  disko.devices = {
+    disk = {
+      nvme = {
+        type = "disk";
+        device = "/dev/nvme0n1";
+        content = {
+          type = "gpt";
+          partitions = {
+            ESP = {
+              size = "512M";
+              type = "EF00";
+              content = {
+                type = "filesystem";
+                format = "vfat";
+                mountpoint = "/boot";
+                mountOptions = [ "umask=0077" ];
+              };
+            };
+            root = {
+              size = "100%";
+              content = {
+                type = "filesystem";
+                format = "ext4";
+                mountpoint = "/";
+              };
+            };
+          };
+        };
+      };
+      games = {
+        type = "disk";
+        device = "/dev/sda";
+        content = {
+          type = "gpt";
+          partitions = {
+            games = {
+              size = "100%";
+              content = {
+                type = "filesystem";
+                format = "ext4";
+                mountpoint = "/mnt/games";
+              };
+            };
+          };
+        };
+      };
+      storage1 = {
+        type = "disk";
+        device = "/dev/sdb";
+        content = {
+          type = "gpt";
+          partitions = {
+            storage1 = {
+              size = "100%";
+              content = {
+                type = "filesystem";
+                format = "ext4";
+                mountpoint = "/mnt/storage1";
+              };
+            };
+          };
+        };
+      };
+      storage2 = {
+        type = "disk";
+        device = "/dev/sdc";
+        content = {
+          type = "gpt";
+          partitions = {
+            storage2 = {
+              size = "100%";
+              content = {
+                type = "filesystem";
+                format = "ext4";
+                mountpoint = "/mnt/storage2";
+              };
+            };
+          };
+        };
+      };
+    };
+  };
+}