feat(dank): enable DMS/niri session on mibook, pin HM to release-26.05, drop redundant keybinds

- Pin home-manager input to release-26.05 to match nixpkgs (was resolving
  to HM master / 26.11, causing a Home Manager version mismatch warning).
- Drop niri.enableKeybinds = true from the dank HM config; keybinds are
  already provided by the imported DMS niri homeModule (includes), and using
  both together triggered the "enableKeybinds and includes.enable" warning.
- Enable my.profiles.dank on mibook (machines/mibook/environments.nix).
- Rebuild confirmed exit 0 with both target warnings resolved.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018Sv2QAunLcLo3tS1YsfLgN

modules/environments/dank/default.nix

@@ -27,7 +27,7 @@ in
       quickshell.package = pkgs.unstable.quickshell;
     };
 
-    # Home side: DMS shell + niri keybinds/spawn for finn.
+    # Home side: DMS shell + niri spawn for finn (keybinds come via includes).
     home-manager.users.finn = {
       imports = [
         inputs.niri.homeModules.niri
@@ -39,7 +39,6 @@ in
         enable = true;
         systemd.enable = true;
         quickshell.package = pkgs.unstable.quickshell;
-        niri.enableKeybinds = true;
         niri.enableSpawn = true;
       };