fix(nix): Apply package overlay to node configurations

- Add self.overlays.default to node01/02/03 configurations
- Makes service packages (chainfire-server, flaredb-server, etc.) available to NixOS modules
- Fixes "chainfire-server package not found" error during nixos-anywhere deployment

Root cause: NixOS modules reference pkgs.chainfire-server but packages were not in pkgs scope
Solution: Apply overlay that injects flake packages into nixpkgs

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

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

.gitignore

@@ -4,7 +4,7 @@
 # Rust
 target/
 **/*.rs.bk
-Cargo.lock
+# Note: Cargo.lock IS tracked for reproducible Nix builds
 
 # Nix
 result

flake.nix

@@ -415,6 +415,7 @@
             disko.nixosModules.disko
             ./docs/por/T036-vm-cluster-deployment/node01/configuration.nix
             self.nixosModules.default
+            { nixpkgs.overlays = [ self.overlays.default ]; }
           ];
         };
 
@@ -424,6 +425,7 @@
             disko.nixosModules.disko
             ./docs/por/T036-vm-cluster-deployment/node02/configuration.nix
             self.nixosModules.default
+            { nixpkgs.overlays = [ self.overlays.default ]; }
           ];
         };
 
@@ -433,6 +435,7 @@
             disko.nixosModules.disko
             ./docs/por/T036-vm-cluster-deployment/node03/configuration.nix
             self.nixosModules.default
+            { nixpkgs.overlays = [ self.overlays.default ]; }
           ];
         };
       };