feat: add NixOS configuration with direnv support

- Add flake.nix with dev shell
- Add NixOS module for Azion runtime config
- Add direnv .envrc for auto-activation
- Update .gitignore with .p*, result, .worktrees/, docs/, .direnv/

flake.lock

@@ -0,0 +1,27 @@
+{
+  "nodes": {
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1777077449,
+        "narHash": "sha256-AIiMJiqvGrN4HyLEbKAoCSRRYn0rnlW5VbKNIMIYqm4=",
+        "owner": "nixos",
+        "repo": "nixpkgs",
+        "rev": "a4bf06618f0b5ee50f14ed8f0da77d34ecc19160",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nixos",
+        "ref": "nixos-25.11",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "nixpkgs": "nixpkgs"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}