fix: drop nested nix develop in website-build to preserve env vars

HUGO_PARAMS_GITVERSION was stripped when website-build called
'nix develop --command hugo' from within an already-active nix shell
(nested nix develop resets the environment). Hugo is already on PATH
from the outer 'nix develop --command task website-deploy' in CI, and
locally tasks run from within 'nix develop' per AGENTS.md convention.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Taskfile.yml

@@ -334,7 +334,7 @@ tasks:
       HUGO_PARAMS_GITVERSION:
         sh: git rev-parse --short HEAD
     cmds:
-      - nix develop --command hugo --source website --minify
+      - hugo --source website --minify
 
   website-verify:
     desc: Check that the deployed site serves the current git version