Style every MFA screen through the element system

The MFA pages (manage, TOTP activate/deactivate, recovery codes, security keys,
reauthenticate) are built almost entirely from allauth's `element` primitives, so
they are styled by overriding the elements rather than by rewriting eight page
templates. New allauth pages then inherit the look for free.

- field + img elements were missing entirely, so allauth fell back to bare HTML:
  the TOTP secret and recovery-code list rendered as unstyled inputs. The QR now
  sits on a white plate -- it is dark modules on a transparent ground, so on the
  dark theme it was dark-on-dark and phones could not scan it.
- button now honours the tags allauth sets. They were all flattened to
  btn-primary, which made "Deactivate" look exactly as safe as "View".
- the `code` field renders as a daisyUI otp wherever it appears, so the
  reauthenticate and activate pages get the same input as the login challenge.
  The boxes step aside past six characters: allauth accepts a TOTP code (6) or a
  recovery code (8) in that one field.

Fixes a crash: the security-key list does {% load humanize %}, which raised
TemplateSyntaxError because django.contrib.humanize was not installed. That page
500'd on every request; it is now installed and covered by a test.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

templates/allauth/elements/button.html

@@ -1,7 +1,15 @@
 {% load allauth %}
+
+{% comment %}
+    allauth tags every button it renders, and mapping those tags is what styles the MFA
+    and account pages without overriding each one. The ranking matters: those pages put
+    three buttons in a row (Deactivate / View / Download) and rely on the tags to say
+    which is destructive and which is secondary. Flattening them all to btn-primary makes
+    "Deactivate" look exactly as safe as "View".
+{% endcomment %}
 {% comment %} djlint:off {% endcomment %}
 <{% if attrs.href %}a href="{{ attrs.href }}"{% else %}button{% endif %}
-class="btn {% if attrs.tags and 'danger' in attrs.tags %}btn-error{% elif attrs.tags and 'secondary' in attrs.tags %}btn-ghost{% elif attrs.tags and 'link' in attrs.tags %}btn-link{% else %}btn-primary{% endif %}"
+class="btn {% if attrs.tags and 'danger' in attrs.tags %}btn-error{% elif attrs.tags and 'link' in attrs.tags %}btn-link{% elif attrs.tags and 'secondary' in attrs.tags %}btn-outline btn-neutral{% elif attrs.tags and 'outline' in attrs.tags %}btn-outline btn-primary{% else %}btn-primary{% endif %}"
 {% if attrs.form %}form="{{ attrs.form }}"{% endif %}
 {% if attrs.id %}id="{{ attrs.id }}"{% endif %}
 {% if attrs.name %}name="{{ attrs.name }}"{% endif %}