chore(flake): refresh nixpkgs inputs to 2026-09-11

Bump nixpkgs and nixpkgs-latest from 2026-05/2026-08 to current
nixos-unstable (2026-09-11); both inputs now resolve to the same rev.
Re-validated every package against the new inputs.

Fallout fixed:
- freetoken: upstream pins torch>=2.11,<2.12 and triton==3.6.0, but the new
  nixpkgs only ships torch 2.13 / triton 3.7. Add a nixpkgs-torch211 input
  pinned at the previous revision and build freetoken against it, keeping
  the CUDA 12.9 / torch 2.11 stack unchanged.
- graphify: nixpkgs' pybloomfilter3 0.7.3 ships sdist metadata that still
  says 0.7.2, tripping pythonMetadataCheckPhase; skip that check only.

All 22 packages build and `nix flake check --no-build` passes.

packages/freetoken/default.nix

@@ -1,5 +1,10 @@
 {
   pkgs,
+  inputs,
   ...
 }:
-pkgs.callPackage ./package.nix { }
+# freetoken pins torch>=2.11,<2.12 and triton==3.6.0, but current
+# nixos-unstable ships torch 2.13 + triton 3.7 and no older torch. Build it
+# with the pinned nixpkgs-torch211 revision (CUDA 12.9 / torch-bin 2.11).
+inputs.nixpkgs-torch211.legacyPackages.${pkgs.stdenv.hostPlatform.system}.callPackage ./package.nix
+  { }