feat(flake): add nixpkgs-qt input for qt5webengine packages

Add separate nixpkgs input for qt5webengine-dependent packages like
jellyfin-media-player. This input updates on a separate Renovate
schedule from main nixpkgs to avoid massive qt5webengine rebuilds
when updating other packages.

- Add nixpkgs-qt input pinned to nixos-25.11
- Create pkgs.qt-pinned overlay namespace

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

flake.lock

@@ -258,6 +258,22 @@
         "type": "github"
       }
     },
+    "nixpkgs-qt": {
+      "locked": {
+        "lastModified": 1770464364,
+        "narHash": "sha256-z5NJPSBwsLf/OfD8WTmh79tlSU8XgIbwmk6qB1/TFzY=",
+        "owner": "nixos",
+        "repo": "nixpkgs",
+        "rev": "23d72dabcb3b12469f57b37170fcbc1789bd7457",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nixos",
+        "ref": "nixos-25.11",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
     "nixpkgs-unstable": {
       "locked": {
         "lastModified": 1769170682,
@@ -347,6 +363,7 @@
         "nix-darwin": "nix-darwin",
         "nix-doom-emacs-unstraightened": "nix-doom-emacs-unstraightened",
         "nixpkgs": "nixpkgs",
+        "nixpkgs-qt": "nixpkgs-qt",
         "nixpkgs-unstable": "nixpkgs-unstable",
         "perles": "perles",
         "plasma-manager": "plasma-manager",

flake.nix

@@ -4,6 +4,9 @@
   inputs = {
     nixpkgs.url = "github:nixos/nixpkgs/nixos-25.11";
     nixpkgs-unstable.url = "github:nixos/nixpkgs/nixos-unstable";
+    # Separate nixpkgs for qt5webengine-dependent packages (jellyfin-media-player, etc.)
+    # Updates on separate Renovate schedule to avoid massive qt rebuilds
+    nixpkgs-qt.url = "github:nixos/nixpkgs/nixos-25.11";
 
     nix-darwin = {
       url = "github:nix-darwin/nix-darwin/nix-darwin-25.11";
@@ -76,6 +79,11 @@
         config.allowUnfree = true;
         overlays = unstableOverlays;
       };
+      # Separate nixpkgs for qt5webengine-heavy packages to avoid rebuild churn
+      qt-pinned = import inputs.nixpkgs-qt {
+        system = prev.stdenv.hostPlatform.system;
+        config.allowUnfree = true;
+      };
       custom = prev.callPackage ./packages {};
       # Compatibility: bitwarden renamed to bitwarden-desktop in unstable
       bitwarden-desktop = prev.bitwarden-desktop or prev.bitwarden;