wgt01: real .mdl/.wok export via Neverblender

Neverblender is installed + enabled in this machine's Blender 4.0.2 config and
confirmed working headless via the flake. Add generator/export_mdl.py:
assembles each tile as a Neverblender-native model (AuroraBase dummy/tile,
trimesh, single aabb walkmesh) in its own scene and calls scene.nvb_mdlexport
to emit real ASCII <resref>.mdl + <resref>.wok for all 40 tiles.

Walkmesh surfacemats via create_wok_materials() slot order (walkable Stone=4,
Nonwalk=7) -> verified correct per tile (CP1 all 4, CN1 all 7, BR_1/CE_S mixed).

flake.nix: add `export` app (nix run .#export -- <blend> <outdir> [CODE...]).
AGENTS.md: record the Neverblender node/surfacemat facts and the kit's tools;
note the slot-index (not material-name) surfacemat gotcha.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

wgt01/flake.nix

@@ -44,6 +44,20 @@
         runtimeInputs = [ py ];
         text = ''exec python ${gen}/make_wok.py "$@"'';
       };
+
+      # Real .mdl + .wok export via the Neverblender addon (must be enabled in
+      # this Blender's user config — confirmed working headless).
+      mkmdl = pkgs.writeShellApplication {
+        name = "wgt-export";
+        runtimeInputs = [ blender ];
+        text = ''
+          blend="''${1:?usage: wgt-export <blend> <outdir> [CODE...]}"
+          outdir="''${2:-mdl}"
+          shift 2 || true
+          exec blender-4.0.2 --background "$blend" --python ${gen}/export_mdl.py \
+            --python-exit-code 1 -- "$outdir" "$@"
+        '';
+      };
     in
     {
       packages.${system}.default = build;
@@ -65,6 +79,10 @@
           type = "app";
           program = "${mkwok}/bin/wgt-wok";
         };
+        export = {
+          type = "app";
+          program = "${mkmdl}/bin/wgt-export";
+        };
       };
 
       devShells.${system}.default = pkgs.mkShell {