Wrap T3 Code apps with optional agent CLI paths

- Split base desktop/server derivations from wrapper layers
- Add optional PATH injection for codex, claudeCode, and opencode
- Update flake inputs and lock entries for nixpkgs/llm-agents

flake.lock

@@ -101,9 +101,7 @@
         "blueprint": "blueprint",
         "bun2nix": "bun2nix",
         "flake-parts": "flake-parts",
-        "nixpkgs": [
-          "nixpkgs"
-        ],
+        "nixpkgs": "nixpkgs",
         "systems": "systems",
         "treefmt-nix": "treefmt-nix"
       },
@@ -122,6 +120,22 @@
       }
     },
     "nixpkgs": {
+      "locked": {
+        "lastModified": 1776949667,
+        "narHash": "sha256-GMSVw35Q+294GlrTUKlx087E31z7KurReQ1YHSKp5iw=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "01fbdeef22b76df85ea168fbfe1bfd9e63681b30",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixpkgs-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "nixpkgs_2": {
       "locked": {
         "lastModified": 1776734388,
         "narHash": "sha256-vl3dkhlE5gzsItuHoEMVe+DlonsK+0836LIRDnm6MXQ=",
@@ -140,7 +154,7 @@
     "root": {
       "inputs": {
         "llm-agents": "llm-agents",
-        "nixpkgs": "nixpkgs",
+        "nixpkgs": "nixpkgs_2",
         "t3code": "t3code"
       }
     },