Added new recipe to justfile

- upload-image recipe added to upload built images
- Added .env file to hold Linode API token
- Update .gitignore file to ignore local changes of .env

.gitignore

@@ -1 +1,2 @@
 result
+.env

flake.lock

@@ -2,11 +2,11 @@
   "nodes": {
     "nixpkgs": {
       "locked": {
-        "lastModified": 1764316264,
-        "narHash": "sha256-82L+EJU+40+FIdeG4gmUlOF1jeSwlf2AwMarrpdHF6o=",
+        "lastModified": 1756469547,
+        "narHash": "sha256-YvtD2E7MYsQ3r7K9K2G7nCslCKMPShoSEAtbjHLtH0k=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "9a7b80b6f82a71ea04270d7ba11b48855681c4b0",
+        "rev": "41d292bfc37309790f70f4c120b79280ce40af16",
         "type": "github"
       },
       "original": {