Fix hugo layout in hugo > ~0.130.0

For some reason, newer hugo versions have trouble with .summary, and on
some pages where .summary is not defined in the page header metadata,
when rendering the page as a preview card, hugo swallows the card's
closing </div> tag. Such a weird bug, we now just work around it by
explicitly setting the .summary meta on pages that cause this bug(?) to
surface.

deploy.py

@@ -18,7 +18,8 @@ if __name__ == '__main__':
         try:
             env = dict(os.environ)
             env['PATH'] = f'{Path("hack").absolute()}:{env["PATH"]}'
-            subprocess.run(['hugo'], cwd=tmpdir, check=True, env=env)
+            hugo = os.environ.get('HUGO', 'hugo')
+            subprocess.run([hugo], cwd=tmpdir, check=True, env=env)
             subprocess.run([pagefind, '--site', 'public'], cwd=tmpdir, check=True, env=env)
             subprocess.run(['git', 'add', '--force', 'public'], cwd=tmpdir, check=True)
             write_tree = subprocess.run(['git', 'write-tree', '--prefix=public/'], cwd=tmpdir, check=True, capture_output=True)