add data/services.nix for shared service definitions

Creates a standalone data file that can be imported by both
aspects/constants.nix and terranix configurations.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

flake.lock

@@ -453,6 +453,21 @@
         "type": "github"
       }
     },
+    "import-tree": {
+      "locked": {
+        "lastModified": 1763762820,
+        "narHash": "sha256-ZvYKbFib3AEwiNMLsejb/CWs/OL/srFQ8AogkebEPF0=",
+        "owner": "vic",
+        "repo": "import-tree",
+        "rev": "3c23749d8013ec6daa1d7255057590e9ca726646",
+        "type": "github"
+      },
+      "original": {
+        "owner": "vic",
+        "repo": "import-tree",
+        "type": "github"
+      }
+    },
     "niri": {
       "inputs": {
         "nixpkgs": "nixpkgs_4",
@@ -932,6 +947,7 @@
         "flake-parts": "flake-parts",
         "home-manager": "home-manager_2",
         "impermanence": "impermanence",
+        "import-tree": "import-tree",
         "niri": "niri",
         "niri-flake": "niri-flake",
         "nix-ai-tools": "nix-ai-tools",