chore(flake): add nixvim input

Declarative Neovim, on the nixos-26.05 release branch and following our
nixpkgs to keep a single nixpkgs in the closure. Consumed by
lyrathorpe/home/editor.nix.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

flake.lock

@@ -106,6 +106,27 @@
         "type": "github"
       }
     },
+    "flake-parts_2": {
+      "inputs": {
+        "nixpkgs-lib": [
+          "nixvim",
+          "nixpkgs"
+        ]
+      },
+      "locked": {
+        "lastModified": 1778716662,
+        "narHash": "sha256-m1Yf0wZ8j1OHjTc2UwHwyQRSnNeSgLJOd7q5Y45hzi4=",
+        "owner": "hercules-ci",
+        "repo": "flake-parts",
+        "rev": "f7c1a2d347e4c52d5fb8d10cb4d94b5884e546fb",
+        "type": "github"
+      },
+      "original": {
+        "owner": "hercules-ci",
+        "repo": "flake-parts",
+        "type": "github"
+      }
+    },
     "git-hooks": {
       "inputs": {
         "flake-compat": "flake-compat",
@@ -303,6 +324,29 @@
         "type": "github"
       }
     },
+    "nixvim": {
+      "inputs": {
+        "flake-parts": "flake-parts_2",
+        "nixpkgs": [
+          "nixpkgs"
+        ],
+        "systems": "systems"
+      },
+      "locked": {
+        "lastModified": 1781038653,
+        "narHash": "sha256-MxUVyE7A5QMJXOEFQhOHsqs4UPhujeDgdFhguE7Wmic=",
+        "owner": "nix-community",
+        "repo": "nixvim",
+        "rev": "e7ce6708cc5b6275406a8feee06ca50c5cafd6bf",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nix-community",
+        "ref": "nixos-26.05",
+        "repo": "nixvim",
+        "type": "github"
+      }
+    },
     "root": {
       "inputs": {
         "firefox-addons": "firefox-addons",
@@ -316,9 +360,25 @@
         "nixos-wsl": "nixos-wsl",
         "nixpkgs": "nixpkgs",
         "nixpkgs-unstable": "nixpkgs-unstable",
+        "nixvim": "nixvim",
         "treefmt-nix": "treefmt-nix"
       }
     },
+    "systems": {
+      "locked": {
+        "lastModified": 1681028828,
+        "narHash": "sha256-Vy1rq5AaRuLzOxct8nz4T6wlgyUR7zLU309k9mBC768=",
+        "owner": "nix-systems",
+        "repo": "default",
+        "rev": "da67096a3b9bf56a91d16901293e51ba5b49a27e",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nix-systems",
+        "repo": "default",
+        "type": "github"
+      }
+    },
     "treefmt-nix": {
       "inputs": {
         "nixpkgs": [