Flake: Add nixpkgs-stable input, put the overlays in the correct place and add jetbrains.rider overlay

Jetbrains apps are currently broken on unstable because of a
jetbrains.jdk buildfailure

flake.lock

@@ -718,6 +718,22 @@
         "type": "github"
       }
     },
+    "nixpkgs-stable": {
+      "locked": {
+        "lastModified": 1753115646,
+        "narHash": "sha256-yLuz5cz5Z+sn8DRAfNkrd2Z1cV6DaYO9JMrEz4KZo/c=",
+        "owner": "nixos",
+        "repo": "nixpkgs",
+        "rev": "92c2e04a475523e723c67ef872d8037379073681",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nixos",
+        "ref": "nixos-25.05",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
     "nixpkgs_2": {
       "locked": {
         "lastModified": 1752950548,
@@ -889,6 +905,7 @@
         "nix-alien": "nix-alien",
         "nix-flatpak": "nix-flatpak",
         "nixpkgs": "nixpkgs_2",
+        "nixpkgs-stable": "nixpkgs-stable",
         "nixvim": "nixvim",
         "nps": "nps",
         "nur": "nur",