nixos: Use codex-cli-nix and claude-code-nix flakes with cachix

Switch from manual version overrides to dedicated flakes:
- github:sadjow/codex-cli-nix for codex
- github:sadjow/claude-code-nix for claude-code

Added cachix substituters and keys for pre-built binaries.

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

nixos/flake.nix

@@ -126,6 +126,16 @@
 
     nixtheplanet.url = "github:matthewcroughan/nixtheplanet";
 
+    codex-cli-nix = {
+      url = "github:sadjow/codex-cli-nix";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
+
+    claude-code-nix = {
+      url = "github:sadjow/claude-code-nix";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
+
   };
 
   outputs = inputs @ {
@@ -353,11 +363,15 @@
         "http://192.168.1.26:5050"
         "https://cache.flox.dev"
         "https://org-agenda-api.cachix.org"
+        "https://codex-cli.cachix.org"
+        "https://claude-code.cachix.org"
       ];
       extra-trusted-public-keys = [
         "1896Folsom.duckdns.org:U2FTjvP95qwAJo0oGpvmUChJCgi5zQoG1YisoI08Qoo="
         "flox-cache-public-1:7F4OyH7ZCnFhcze3fJdfyXYLQw/aV7GEed86nQ7IsOs="
         "org-agenda-api.cachix.org-1:liKFemKkOLV/rJt2txDNcpDjRsqLuBneBjkSw/UVXKA="
+        "codex-cli.cachix.org-1:1Br3H1hHoRYG22n//cGKJOk3cQXgYobUel6O8DgSing="
+        "claude-code.cachix.org-1:YeXf2aNu7UTX8Vwrze0za1WEDS+4DuI2kVeWEE4fsRk="
       ];
     };
     nixosConfigurations =